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< p > < strong > 原视频地址:< / strong > < a target = "_blank" rel = "noopener" href = "https://www.bilibili.com/video/BV1Kr4y1i7ru/?share_source=copy_web&vd_source=aee5e475191b69e6c781059ab6662584" > 黑马程序员 MySQL数据库入门到精通， < / a > < / p >
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< h1 id = "一-Mysql入门" > < a href = "#一-Mysql入门" class = "headerlink" title = "一.Mysql入门" > < / a > 一.Mysql入门< / h1 > < h2 id = "1-SQL" > < a href = "#1-SQL" class = "headerlink" title = "1.SQL" > < / a > 1.SQL< / h2 > < p > 全称 Structured Query Language， ， < / p >
< h3 id = "1-1-SQL通用语法" > < a href = "#1-1-SQL通用语法" class = "headerlink" title = "1.1 SQL通用语法" > < / a > 1.1 SQL通用语法< / h3 > < p > < img src = "/pictures/image-20230926220120609.png" alt = "image-20230926220120609" > < / p >
< h3 id = "1-2-SQL分类" > < a href = "#1-2-SQL分类" class = "headerlink" title = "1.2 SQL分类" > < / a > 1.2 SQL分类< / h3 > < p > < img src = "/pictures/image-20230926215941275.png" alt = "image-20230926215941275" > < / p >
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< h3 id = "1-3-DDL-数据定义语言" > < a href = "#1-3-DDL-数据定义语言" class = "headerlink" title = "1.3 DDL-数据定义语言" > < / a > 1.3 DDL-数据定义语言< / h3 > < p > < strong > 连接本地mysql的命令< / strong > < / p >
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< figure class = "highlight shell" > < table > < tr > < td class = "gutter" > < pre > < span class = "line" > 1< / span > < br > < / pre > < / td > < td class = "code" > < pre > < span class = "line" > mysql -u root -p< / span > < br > < / pre > < / td > < / tr > < / table > < / figure >
< p > < strong > 常用的DDL操作< / strong > < / p >
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< figure class = "highlight sql" > < table > < tr > < td class = "gutter" > < pre > < span class = "line" > 1< / span > < br > < span class = "line" > 2< / span > < br > < span class = "line" > 3< / span > < br > < span class = "line" > 4< / span > < br > < span class = "line" > 5< / span > < br > < span class = "line" > 6< / span > < br > < span class = "line" > 7< / span > < br > < span class = "line" > 8< / span > < br > < span class = "line" > 9< / span > < br > < span class = "line" > 10< / span > < br > < span class = "line" > 11< / span > < br > < span class = "line" > 12< / span > < br > < span class = "line" > 13< / span > < br > < span class = "line" > 14< / span > < br > < span class = "line" > 15< / span > < br > < span class = "line" > 16< / span > < br > < span class = "line" > 17< / span > < br > < span class = "line" > 18< / span > < br > < span class = "line" > 19< / span > < br > < span class = "line" > 20< / span > < br > < span class = "line" > 21< / span > < br > < span class = "line" > 22< / span > < br > < span class = "line" > 23< / span > < br > < span class = "line" > 24< / span > < br > < span class = "line" > 25< / span > < br > < span class = "line" > 26< / span > < br > < span class = "line" > 27< / span > < br > < span class = "line" > 28< / span > < br > < span class = "line" > 29< / span > < br > < span class = "line" > 30< / span > < br > < span class = "line" > 31< / span > < br > < span class = "line" > 32< / span > < br > < span class = "line" > 33< / span > < br > < span class = "line" > 34< / span > < br > < span class = "line" > 35< / span > < br > < span class = "line" > 36< / span > < br > < span class = "line" > 37< / span > < br > < span class = "line" > 38< / span > < br > < span class = "line" > 39< / span > < br > < span class = "line" > 40< / span > < br > < span class = "line" > 41< / span > < br > < span class = "line" > 42< / span > < br > < span class = "line" > 43< / span > < br > < span class = "line" > 44< / span > < br > < span class = "line" > 45< / span > < br > < span class = "line" > 46< / span > < br > < span class = "line" > 47< / span > < br > < span class = "line" > 48< / span > < br > < span class = "line" > 49< / span > < br > < span class = "line" > 50< / span > < br > < span class = "line" > 51< / span > < br > < span class = "line" > 52< / span > < br > < span class = "line" > 53< / span > < br > < span class = "line" > 54< / span > < br > < span class = "line" > 55< / span > < br > < span class = "line" > 56< / span > < br > < span class = "line" > 57< / span > < br > < span class = "line" > 58< / span > < br > < span class = "line" > 59< / span > < br > < span class = "line" > 60< / span > < br > < span class = "line" > 61< / span > < br > < span class = "line" > 62< / span > < br > < span class = "line" > 63< / span > < br > < span class = "line" > 64< / span > < br > < / pre > < / td > < td class = "code" > < pre > < span class = "line" > < span class = "comment" > -- ------------------------------------------------------数据库的操作------------------------------------------------------------------------< / span > < / span > < br > < span class = "line" > < span class = "comment" > -- 展示所有的数据库< / span > < / span > < br > < span class = "line" > < span class = "keyword" > show< / span > databases ;< / span > < br > < span class = "line" > < / span > < br > < span class = "line" > < span class = "comment" > -- 查询当前的数据库< / span > < / span > < br > < span class = "line" > < span class = "keyword" > select< / span > database();< / span > < br > < span class = "line" > < / span > < br > < span class = "line" > < span class = "comment" > -- 创建数据库< / span > < / span > < br > < span class = "line" > < span class = "keyword" > create< / span > database if < span class = "keyword" > not< / span > < span class = "keyword" > exists< / span > itcast;< / span > < br > < span class = "line" > < / span > < br > < span class = "line" > < span class = "comment" > -- 删除数据库< / span > < / span > < br > < span class = "line" > < span class = "keyword" > drop< / span > database if < span class = "keyword" > exists< / span > itcast;< / span > < br > < span class = "line" > < / span > < br > < span class = "line" > < span class = "comment" > -- 使用数据库< / span > < / span > < br > < span class = "line" > use itcast;< / span > < br > < span class = "line" > < / span > < br > < span class = "line" > < / span > < br > < span class = "line" > < span class = "comment" > -- ----------------------------------------------------------表的操作--------------------------------------------------------------------< / span > < / span > < br > < span class = "line" > < / span > < br > < span class = "line" > < span class = "comment" > -- 创建用户表< / span > < / span > < br > < span class = "line" > < span class = "keyword" > create< / span > < span class = "keyword" > table< / span > tb_user(id < span class = "type" > int< / span > comment < span class = "string" > ' 编号' < / span > , name < span class = "type" > varchar< / span > (< span class = "number" > 50< / span > ) comment < span class = "string" > ' 姓名' < / span > , age < span class = "type" > int< / span > comment < span class = "string" > ' 年龄'
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< p > < strong > Mysql的数据类型< / strong > < / p >
< p > 数值数据类型< / p >
< p > < img src = "/pictures/image-20230926224723586.png" alt = "image-20230926224723586" > < / p >
< p > 字符串数据类型< / p >
< p > < img src = "/pictures/image-20230926224755542.png" alt = "image-20230926224755542" > < / p >
< p > 日期时间类型< / p >
< p > < img src = "/pictures/image-20230926224539052.png" alt = "image-20230926224539052" > < / p >
2023-10-01 20:51:27 +08:00
< h3 id = "1-4-DML-数据操作语言" > < a href = "#1-4-DML-数据操作语言" class = "headerlink" title = "1.4 DML-数据操作语言" > < / a > 1.4 DML-数据操作语言< / h3 > < figure class = "highlight sql" > < table > < tr > < td class = "gutter" > < pre > < span class = "line" > 1< / span > < br > < span class = "line" > 2< / span > < br > < span class = "line" > 3< / span > < br > < span class = "line" > 4< / span > < br > < span class = "line" > 5< / span > < br > < span class = "line" > 6< / span > < br > < span class = "line" > 7< / span > < br > < span class = "line" > 8< / span > < br > < span class = "line" > 9< / span > < br > < span class = "line" > 10< / span > < br > < span class = "line" > 11< / span > < br > < span class = "line" > 12< / span > < br > < span class = "line" > 13< / span > < br > < span class = "line" > 14< / span > < br > < span class = "line" > 15< / span > < br > < span class = "line" > 16< / span > < br > < span class = "line" > 17< / span > < br > < span class = "line" > 18< / span > < br > < span class = "line" > 19< / span > < br > < span class = "line" > 20< / span > < br > < span class = "line" > 21< / span > < br > < span class = "line" > 22< / span > < br > < / pre > < / td > < td class = "code" > < pre > < span class = "line" > < span class = "comment" > -- ------------------------------------------------DML-增删改操作---------------------------------------------------< / span > < / span > < br > < span class = "line" > < span class = "comment" > -- 添加数据< / span > < / span > < br > < span class = "line" > < span class = "keyword" > select< / span > database();< / span > < br > < span class = "line" > < span class = "keyword" > show< / span > tables;< / span > < br > < span class = "line" > < span class = "comment" > -- 该指定的字段添加数据< / span > < / span > < br > < span class = "line" > < span class = "keyword" > insert< / span > < span class = "keyword" > into< / span > employee(id, workno, name, gender, age, idcard, entrydate) < span class = "keyword" > value< / span > (< span class = "number" > 1< / span > , < span class = "string" > ' 1' < / span > , < span class = "string" > ' 小华' < / span > , < span class = "string" > ' 男' < / span > , < span class = "number" > 20< / span > , < span class = "string" > ' 123456789123456789' < / span > , < span class = "string" > ' 2001-01-01' < / span > );< / span > < br > < span class = "line" > < span class = "keyword" > select< / span > < span class = "operator" > *< / span > < / span > < br > < span class = "line" > < span class = "keyword" > from< / span > employee;< / span > < br > < span class = "line" > < span class = "comment" > -- 给全部的字段添加数据< / span > < / span > < br > < span class = "line" > < span class = "keyword" > insert< / span > < span class = "keyword" > into< / span > employee < span class = "keyword" > value< / span > (< span class = "number" > 2< / span > , < span class = "string" > ' 2' < / span > , < span class = "string" > ' 小刚' < / span > , < span class = "string" > ' 男' < / span > , < span class = "number" > 23< / span > , < span class = "string" > ' 123456784124456789' < / span > , < span class = "string" > ' 2008-01-01' < / span > );< / span > < br > < span class = "line" > < span class = "comment" > -- 批量添加数据< / span > < / span > < br > < span class = "line" > < span class = "keyword" > insert< / span > < span class = "keyword" > into< / span > employee< / span > < br > < span class = "line" > < span class = "keyword" > values< / span > (< span class = "number" > 3< / span > , < span class = "string" > ' 3' < / span > , < span class = "string" > ' 小李' < / span > , < span class = "string" > ' 男' < / span > , < span class = "number" > 23< / span > , < span class = "string" > ' 123456784124456789' < / span > , < span class = "string" > ' 2008-01-01' < / span > ),< / span > < br > < span class = "line" > (< span class = "number" > 4< / span > , < span class = "string" > ' 4' < / span > , < span class = "string" > ' 小黄' < / span > , < span class = "string" > ' 男' < / span > , < span class = "number" > 23< / span > , < span class = "string" > ' 123456784124456789' < / span > , < span class = "string" > ' 2008-01-01' < / span > );< / span > < br > < span class = "line" > < / span > < br > < span class = "line" > < span class = "comment" > -- 修改数据（不带条件修改所有）< / span > < / span > < br > < span class = "line" > < span class = "keyword" > update< / span > employee < span class = "keyword" > set< / span > name < span class = "operator" > =< / span > < span class = "string" > ' 张三' < / span > < span class = "keyword" > where< / span > id < span class = "operator" > =< / span > < span class = "number" > 1< / span > ;< / span > < br > < span class = "line" > < span class = "keyword" > update< / span > employee < span class = "key
2023-09-30 18:36:25 +08:00
2023-10-01 20:51:27 +08:00
< h3 id = "1-5-DQL-数据查询语言" > < a href = "#1-5-DQL-数据查询语言" class = "headerlink" title = "1.5 DQL-数据查询语言" > < / a > 1.5 DQL-数据查询语言< / h3 > < p > < img src = "/pictures/image-20230930222149036.png" alt = "image-20230930222149036" > < / p >
2023-10-01 16:38:07 +08:00
< ul >
< li > 基本查询（不带任何条件）< / li >
< li > 条件查询（ ） < / li >
< li > 聚合函数（ ） < / li >
< li > 分组查询（ ） < / li >
< li > 排序查询（ ） < / li >
< li > 分页查询（ < / li >
< / ul >
< p > < strong > 测试数据准备< / strong > < / p >
< figure class = "highlight sql" > < table > < tr > < td class = "gutter" > < pre > < span class = "line" > 1< / span > < br > < span class = "line" > 2< / span > < br > < span class = "line" > 3< / span > < br > < span class = "line" > 4< / span > < br > < span class = "line" > 5< / span > < br > < span class = "line" > 6< / span > < br > < span class = "line" > 7< / span > < br > < span class = "line" > 8< / span > < br > < span class = "line" > 9< / span > < br > < span class = "line" > 10< / span > < br > < span class = "line" > 11< / span > < br > < span class = "line" > 12< / span > < br > < span class = "line" > 13< / span > < br > < span class = "line" > 14< / span > < br > < span class = "line" > 15< / span > < br > < span class = "line" > 16< / span > < br > < span class = "line" > 17< / span > < br > < span class = "line" > 18< / span > < br > < span class = "line" > 19< / span > < br > < span class = "line" > 20< / span > < br > < span class = "line" > 21< / span > < br > < span class = "line" > 22< / span > < br > < span class = "line" > 23< / span > < br > < span class = "line" > 24< / span > < br > < span class = "line" > 25< / span > < br > < span class = "line" > 26< / span > < br > < span class = "line" > 27< / span > < br > < span class = "line" > 28< / span > < br > < span class = "line" > 29< / span > < br > < / pre > < / td > < td class = "code" > < pre > < span class = "line" > < span class = "comment" > -- 数据准备< / span > < / span > < br > < span class = "line" > < span class = "keyword" > create< / span > < span class = "keyword" > table< / span > emp(< / span > < br > < span class = "line" > id < span class = "type" > int< / span > comment < span class = "string" > ' 编号' < / span > ,< / span > < br > < span class = "line" > workno < span class = "type" > varchar< / span > (< span class = "number" > 10< / span > ) comment < span class = "string" > ' 工号' < / span > ,< / span > < br > < span class = "line" > name < span class = "type" > varchar< / span > (< span class = "number" > 10< / span > ) comment < span class = "string" > ' 姓名' < / span > ,< / span > < br > < span class = "line" > gender < span class = "type" > char< / span > (< span class = "number" > 1< / span > ) comment < span class = "string" > ' 性别' < / span > ,< / span > < br > < span class = "line" > age tinyint unsigned comment < span class = "string" > ' 年龄' < / span > ,< / span > < br > < span class = "line" > idcard < span class = "type" > char< / span > (< span class = "number" > 18< / span > ) comment < span class = "string" > ' 身份证号' < / span > ,< / span > < br > < span class = "line" > workaddress < span class = "type" > varchar< / span > (< span class = "number" > 50< / span > ) comment < span class = "string" > ' 工作地址' < / span > ,< / span > < br > < span class = "line" > entrydate < span class = "type" > date< / span > comment < span class = "string" > ' 入职时间' < / span > < / span > < br > < span class = "line" > ) comment < span class = "string" > ' 员工表' < / span > ;< / span > < br > < span class = "line" > < span class = "comment" > -- 插入数据< / span > < / span > < br > < span class = "line" > < span class = "keyword" > insert< / span > < span class = "keyword" > into< / span > emp(id, workno, name, gender, age, idcard, workaddress,entrydate)< / span > < br > < span class = "line" > < span class = "keyword" > values< / span > (< span class = "number" > 1< / span > ,< span class = "string" > ' 1' < / span > ,< span class = "string" > ' 柳岩' < / span > ,< span class = "string" > ' 女' < / span > ,< span class = "number" > 20< / span > ,< span class = "string" > ' 12345678912345678' < / span > ,< span class = "string" > ' 北京' < / span > ,< span class = "string" > ' 2001-01-01' < / span > ),< / span > < br > < span class = "line" > (< span class = "number" > 2< / span > ,< span class = "string" > ' 2' < / span > ,< span class = "string" > ' 张无忌' < / span > ,< span class = "string" > ' 男' < / span > ,< span class = "number" > 18< / span > ,< span class = "string" > ' 123456789012345670' < / span > ,< span class = "string" > ' 北京' < / span > ,< span class = "string" > ' 2005-09-01' < / span > ),< / span > < br > < span class = "line" > (< span class = "number" > 3< / span > ,< span class = "string" > ' 3' < / span > ,< span class = "string" > ' 韦一笑' < / span > ,< span class = "string" > ' 男' < / span > ,< span class = "number" > 38< / span > ,< span class = "string" > ' 12345678972345670' < / span > ,< span class = "string" > ' 上海' < / span > ,< span class = "string" > ' 2005-08-01' < / span > ),< / span > < br > < span class = "line" > (< span class = "number" > 4< / span > ,< span class = "string" > ' 4' < / span > ,< span class = "string" > ' 赵敏' < / span > ,< span class = "string" > ' 女& #x27
< h4 id = "1-5-1-基础查询" > < a href = "#1-5-1-基础查询" class = "headerlink" title = "1.5.1 基础查询" > < / a > 1.5.1 基础查询< / h4 > < figure class = "highlight sql" > < table > < tr > < td class = "gutter" > < pre > < span class = "line" > 1< / span > < br > < span class = "line" > 2< / span > < br > < span class = "line" > 3< / span > < br > < span class = "line" > 4< / span > < br > < span class = "line" > 5< / span > < br > < span class = "line" > 6< / span > < br > < span class = "line" > 7< / span > < br > < span class = "line" > 8< / span > < br > < span class = "line" > 9< / span > < br > < span class = "line" > 10< / span > < br > < span class = "line" > 11< / span > < br > < span class = "line" > 12< / span > < br > < span class = "line" > 13< / span > < br > < span class = "line" > 14< / span > < br > < span class = "line" > 15< / span > < br > < span class = "line" > 16< / span > < br > < span class = "line" > 17< / span > < br > < span class = "line" > 18< / span > < br > < span class = "line" > 19< / span > < br > < span class = "line" > 20< / span > < br > < span class = "line" > 21< / span > < br > < span class = "line" > 22< / span > < br > < / pre > < / td > < td class = "code" > < pre > < span class = "line" > < span class = "comment" > -- 查看插入的数据< / span > < / span > < br > < span class = "line" > < span class = "keyword" > select< / span > < span class = "operator" > *< / span > < span class = "keyword" > from< / span > emp;< / span > < br > < span class = "line" > < / span > < br > < span class = "line" > < span class = "comment" > -- 查询指定字段 name workno age 返回< / span > < / span > < br > < span class = "line" > < span class = "keyword" > select< / span > name, workno, age< / span > < br > < span class = "line" > < span class = "keyword" > from< / span > emp;< / span > < br > < span class = "line" > < / span > < br > < span class = "line" > < span class = "comment" > -- 查询所有字段返回< / span > < / span > < br > < span class = "line" > < span class = "keyword" > select< / span > id,< / span > < br > < span class = "line" > workno,< / span > < br > < span class = "line" > name,< / span > < br > < span class = "line" > gender,< / span > < br > < span class = "line" > age,< / span > < br > < span class = "line" > idcard,< / span > < br > < span class = "line" > workaddress,< / span > < br > < span class = "line" > entrydate< / span > < br > < span class = "line" > < span class = "keyword" > from< / span > emp;< / span > < br > < span class = "line" > < / span > < br > < span class = "line" > < span class = "comment" > -- distinct去重关键字< / span > < / span > < br > < span class = "line" > < span class = "comment" > -- 查询所有员工的工作地址(不要重复的地址)< / span > < / span > < br > < span class = "line" > < span class = "keyword" > select< / span > < span class = "keyword" > distinct< / span > workaddress < span class = "string" > ' 工作地址' < / span > < / span > < br > < span class = "line" > < span class = "keyword" > from< / span > emp;< / span > < br > < / pre > < / td > < / tr > < / table > < / figure >
< h4 id = "1-5-2-条件查询" > < a href = "#1-5-2-条件查询" class = "headerlink" title = "1.5.2 条件查询" > < / a > 1.5.2 条件查询< / h4 > < p > 语法: < code > SELECT 字段列表 FROM 表名 WHERE 条件列表 ;< / code > < / p >
< p > < img src = "/pictures/image-20231001154822524.png" alt = "image-20231001154822524" > < / p >
< p > < img src = "/pictures/image-20231001154903121.png" alt = "image-20231001154903121" > < / p >
< p > < strong > 举例< / strong > < / p >
< figure class = "highlight sql" > < table > < tr > < td class = "gutter" > < pre > < span class = "line" > 1< / span > < br > < span class = "line" > 2< / span > < br > < span class = "line" > 3< / span > < br > < span class = "line" > 4< / span > < br > < span class = "line" > 5< / span > < br > < span class = "line" > 6< / span > < br > < span class = "line" > 7< / span > < br > < span class = "line" > 8< / span > < br > < span class = "line" > 9< / span > < br > < span class = "line" > 10< / span > < br > < span class = "line" > 11< / span > < br > < span class = "line" > 12< / span > < br > < span class = "line" > 13< / span > < br > < span class = "line" > 14< / span > < br > < span class = "line" > 15< / span > < br > < span class = "line" > 16< / span > < br > < span class = "line" > 17< / span > < br > < span class = "line" > 18< / span > < br > < span class = "line" > 19< / span > < br > < span class = "line" > 20< / span > < br > < span class = "line" > 21< / span > < br > < span class = "line" > 22< / span > < br > < span class = "line" > 23< / span > < br > < span class = "line" > 24< / span > < br > < span class = "line" > 25< / span > < br > < span class = "line" > 26< / span > < br > < span class = "line" > 27< / span > < br > < span class = "line" > 28< / span > < br > < span class = "line" > 29< / span > < br > < span class = "line" > 30< / span > < br > < span class = "line" > 31< / span > < br > < span class = "line" > 32< / span > < br > < span class = "line" > 33< / span > < br > < span class = "line" > 34< / span > < br > < / pre > < / td > < td class = "code" > < pre > < span class = "line" > < span class = "comment" > -- 条件查询< / span > < / span > < br > < span class = "line" > < span class = "comment" > -- 查询年龄等于 88 的员工< / span > < / span > < br > < span class = "line" > < span class = "keyword" > select< / span > < span class = "operator" > *< / span > < span class = "keyword" > from< / span > emp < span class = "keyword" > where< / span > age < span class = "operator" > =< / span > < span class = "number" > 88< / span > ;< / span > < br > < span class = "line" > < / span > < br > < span class = "line" > < span class = "comment" > -- 查询年龄小于20的员工信息< / span > < / span > < br > < span class = "line" > < span class = "keyword" > select< / span > < span class = "operator" > *< / span > < span class = "keyword" > from< / span > emp < span class = "keyword" > where< / span > age < span class = "operator" > < < / span > < span class = "number" > 20< / span > ;< / span > < br > < span class = "line" > < / span > < br > < span class = "line" > < span class = "comment" > -- 查询年龄小于等于20的员工信息< / span > < / span > < br > < span class = "line" > < span class = "keyword" > select< / span > < span class = "operator" > *< / span > < span class = "keyword" > from< / span > emp < span class = "keyword" > where< / span > age < span class = "operator" > < =< / span > < span class = "number" > 20< / span > ;< / span > < br > < span class = "line" > < / span > < br > < span class = "line" > < span class = "comment" > -- 查询没有身份证号的员工信息< / span > < / span > < br > < span class = "line" > < span class = "keyword" > select< / span > < span class = "operator" > *< / span > < span class = "keyword" > from< / span > emp < span class = "keyword" > where< / span > idcard < span class = "keyword" > is< / span > < span class = "keyword" > null< / span > ;< / span > < br > < span class = "line" > < / span > < br > < span class = "line" > < span class = "comment" > -- 查询年龄不等于88的员工信息(< > 也表示不等于)< / span > < / span > < br > < span class = "line" > < span class = "keyword" > select< / span > < span class = "operator" > *< / span > < span class = "keyword" > from< / span > emp < span class = "keyword" > where< / span > age < span class = "operator" > !=< / span > < span class = "number" > 88< / span > ;< / span > < br > < span class = "line" > < span class = "keyword" > select< / span > < span class = "operator" > *< / span > < span class = "keyword" > from< / span > emp < span class = "keyword" > where< / span > age < span class = "operator" > < > < / span > < span class = "number" > 88< / span > ;< / span > < br > < span class = "line" > < / span > < br > < span class = "line" > < span class = "comment" > -- 查询年龄在15~20(包含)之间的员工信息（三种实现方式）< / span > < / span > < br > < span class = "line" > < span class = "keyword" > select< / span > < span class = "operator" > *< / span > < span class = "keyword" > from< / span > emp < span class = "keyword" > where< / span > age < span class = "operator" > > =< / span > < span class = "number" > 15< / span > < span class = "operator" > & & < / span > age < span class = "operator" > < =< / span > < span class = "number" > 20< / span > ;< / span > < br > < span class = "line" > < span class = "keyword" > select< / span > < span class = "operator" > *< / span > < span class = "keyword" > from< / span > emp < span class = "keyword" > where< / span > age < span class = "operator" > > =< / span > < span class = "number" > 15< / span > < s
< h4 id = "1-5-3-聚合函数" > < a href = "#1-5-3-聚合函数" class = "headerlink" title = "1.5.3 聚合函数" > < / a > 1.5.3 聚合函数< / h4 > < p > 语法: < code > SELECT 聚合函数(字段列表) FROM 表名 ;< / code > < / p >
< blockquote >
< p > 注意 : NULL值是不参与所有聚合函数运算的< / p >
< / blockquote >
< p > < img src = "/pictures/image-20231001160812611.png" alt = "image-20231001160812611" > < / p >
< figure class = "highlight sql" > < table > < tr > < td class = "gutter" > < pre > < span class = "line" > 1< / span > < br > < span class = "line" > 2< / span > < br > < span class = "line" > 3< / span > < br > < span class = "line" > 4< / span > < br > < span class = "line" > 5< / span > < br > < span class = "line" > 6< / span > < br > < span class = "line" > 7< / span > < br > < span class = "line" > 8< / span > < br > < span class = "line" > 9< / span > < br > < span class = "line" > 10< / span > < br > < span class = "line" > 11< / span > < br > < span class = "line" > 12< / span > < br > < span class = "line" > 13< / span > < br > < span class = "line" > 14< / span > < br > < span class = "line" > 15< / span > < br > < span class = "line" > 16< / span > < br > < / pre > < / td > < td class = "code" > < pre > < span class = "line" > < span class = "comment" > -- 聚合函数< / span > < / span > < br > < span class = "line" > < span class = "comment" > -- 统计该企业员工数量(空值是不参与统计的)< / span > < / span > < br > < span class = "line" > < span class = "keyword" > select< / span > < span class = "built_in" > count< / span > (< span class = "operator" > *< / span > ) < span class = "keyword" > from< / span > emp;< / span > < br > < span class = "line" > < span class = "keyword" > select< / span > < span class = "built_in" > count< / span > (idcard) < span class = "keyword" > from< / span > emp;< / span > < br > < span class = "line" > < / span > < br > < span class = "line" > < span class = "comment" > -- 统计该企业员工的平均年龄< / span > < / span > < br > < span class = "line" > < span class = "keyword" > select< / span > < span class = "built_in" > avg< / span > (age) < span class = "keyword" > from< / span > emp;< / span > < br > < span class = "line" > < / span > < br > < span class = "line" > < span class = "comment" > -- 统计该企业员工的最大年龄< / span > < / span > < br > < span class = "line" > < span class = "keyword" > select< / span > < span class = "built_in" > max< / span > (age) < span class = "keyword" > from< / span > emp;< / span > < br > < span class = "line" > < / span > < br > < span class = "line" > < span class = "comment" > -- 统计该企业员工的最小年龄< / span > < / span > < br > < span class = "line" > < span class = "keyword" > select< / span > < span class = "built_in" > min< / span > (age) < span class = "keyword" > from< / span > emp;< / span > < br > < span class = "line" > < / span > < br > < span class = "line" > < span class = "comment" > -- 统计西安地区员工的年龄之和< / span > < / span > < br > < span class = "line" > < span class = "keyword" > select< / span > < span class = "built_in" > sum< / span > (age) < span class = "keyword" > from< / span > emp < span class = "keyword" > where< / span > workaddress < span class = "operator" > =< / span > < span class = "string" > ' 西安' < / span > ;< / span > < br > < / pre > < / td > < / tr > < / table > < / figure >
< h4 id = "1-5-4-分组查询" > < a href = "#1-5-4-分组查询" class = "headerlink" title = "1.5.4 分组查询" > < / a > 1.5.4 分组查询< / h4 > < p > 语法: < code > SELECT 字段列表 FROM 表名 [ WHERE 条件 ] GROUP BY 分组字段名 [ HAVING 分组 后过滤条件 ];< / code > < / p >
< p > < strong > where与having区别< / strong > < / p >
< ul >
< li > 执行时机不同： ， ， ； < / li >
< li > 判断条件不同： ， < / li >
< / ul >
< blockquote >
< p > 注意事项:< br > • 分组之后，查询的字段一般为聚合函数和分组字段，查询其他字段无任何意义。< br > • 执行顺序: where > 聚合函数 > having 。< br > • 支持多字段分组, 具体语法为 : group by columnA,columnB< / p >
< / blockquote >
< p > < img src = "/pictures/image-20231001163315161.png" alt = "image-20231001163315161" > < / p >
< figure class = "highlight sql" > < table > < tr > < td class = "gutter" > < pre > < span class = "line" > 1< / span > < br > < span class = "line" > 2< / span > < br > < span class = "line" > 3< / span > < br > < span class = "line" > 4< / span > < br > < span class = "line" > 5< / span > < br > < span class = "line" > 6< / span > < br > < span class = "line" > 7< / span > < br > < span class = "line" > 8< / span > < br > < span class = "line" > 9< / span > < br > < / pre > < / td > < td class = "code" > < pre > < span class = "line" > < span class = "comment" > -- 分组查询< / span > < / span > < br > < span class = "line" > < span class = "comment" > -- 根据性别分组，统计男性员工和女性员工的数量< / span > < / span > < br > < span class = "line" > < span class = "keyword" > select< / span > gender, < span class = "built_in" > count< / span > (< span class = "operator" > *< / span > ) < span class = "keyword" > from< / span > emp < span class = "keyword" > group< / span > < span class = "keyword" > by< / span > gender;< / span > < br > < span class = "line" > < / span > < br > < span class = "line" > < span class = "comment" > -- 根据性别进行分组，统计男性员工和女性员工的平均年龄< / span > < / span > < br > < span class = "line" > < span class = "keyword" > select< / span > gender, < span class = "built_in" > avg< / span > (age) < span class = "keyword" > from< / span > emp < span class = "keyword" > group< / span > < span class = "keyword" > by< / span > gender;< / span > < br > < span class = "line" > < / span > < br > < span class = "line" > < span class = "comment" > -- 查询年龄小于45岁的员工， ， < / span > < / span > < br > < span class = "line" > < span class = "keyword" > select< / span > workaddress,< span class = "built_in" > count< / span > (< span class = "operator" > *< / span > ) address_count < span class = "keyword" > from< / span > emp < span class = "keyword" > where< / span > age < span class = "operator" > < < / span > < span class = "number" > 45< / span > < span class = "keyword" > group< / span > < span class = "keyword" > by< / span > workaddress < span class = "keyword" > having< / span > address_count < span class = "operator" > > =< / span > < span class = "number" > 3< / span > ;< / span > < br > < / pre > < / td > < / tr > < / table > < / figure >
< h4 id = "1-5-5-排序查询" > < a href = "#1-5-5-排序查询" class = "headerlink" title = "1.5.5 排序查询" > < / a > 1.5.5 排序查询< / h4 > < p > 语法: < code > SELECT 字段列表 FROM 表名 ORDER BY 字段1 排序方式1 , 字段2 排序方式2 ;< / code > < / p >
< blockquote >
< p > 注意事项：< br > • 如果是升序, 可以不指定排序方式ASC， < br > • 如果是多字段排序，当第一个字段值相同时，才会根据第二个字段进行排序 ;< / p >
< / blockquote >
2023-10-01 20:51:27 +08:00
< figure class = "highlight sql" > < table > < tr > < td class = "gutter" > < pre > < span class = "line" > 1< / span > < br > < span class = "line" > 2< / span > < br > < span class = "line" > 3< / span > < br > < span class = "line" > 4< / span > < br > < span class = "line" > 5< / span > < br > < span class = "line" > 6< / span > < br > < span class = "line" > 7< / span > < br > < span class = "line" > 8< / span > < br > < span class = "line" > 9< / span > < br > < span class = "line" > 10< / span > < br > < span class = "line" > 11< / span > < br > < / pre > < / td > < td class = "code" > < pre > < span class = "line" > < span class = "comment" > -- 排序查询< / span > < / span > < br > < span class = "line" > < span class = "comment" > -- 根据年龄对公司的员工进行升序排序(asc可以省略)< / span > < / span > < br > < span class = "line" > < span class = "keyword" > select< / span > < span class = "operator" > *< / span > < span class = "keyword" > from< / span > emp < span class = "keyword" > order< / span > < span class = "keyword" > by< / span > age ;< / span > < br > < span class = "line" > < span class = "comment" > -- 降序排序< / span > < / span > < br > < span class = "line" > < span class = "keyword" > select< / span > < span class = "operator" > *< / span > < span class = "keyword" > from< / span > emp < span class = "keyword" > order< / span > < span class = "keyword" > by< / span > age < span class = "keyword" > desc< / span > ;< / span > < br > < span class = "line" > < / span > < br > < span class = "line" > < span class = "comment" > -- 根据员工的入职时间降序排序< / span > < / span > < br > < span class = "line" > < span class = "keyword" > select< / span > < span class = "operator" > *< / span > < span class = "keyword" > from< / span > emp < span class = "keyword" > order< / span > < span class = "keyword" > by< / span > entrydate < span class = "keyword" > desc< / span > ;< / span > < br > < span class = "line" > < / span > < br > < span class = "line" > < span class = "comment" > -- 根据员工的年龄升序排序，年龄相同，再按照入职时间进行降序排序< / span > < / span > < br > < span class = "line" > < span class = "keyword" > select< / span > < span class = "operator" > *< / span > < span class = "keyword" > from< / span > emp < span class = "keyword" > order< / span > < span class = "keyword" > by< / span > age < span class = "keyword" > asc< / span > ,entrydate < span class = "keyword" > desc< / span > ;< / span > < br > < / pre > < / td > < / tr > < / table > < / figure >
< h4 id = "1-5-6-分页查询" > < a href = "#1-5-6-分页查询" class = "headerlink" title = "1.5.6 分页查询" > < / a > 1.5.6 分页查询< / h4 > < p > 语法: < code > SELECT 字段列表 FROM 表名 LIMIT 起始索引, 查询记录数 ;< / code > < / p >
< blockquote >
< p > 注意事项:< br > • 起始索引从0开始， = （查询页码 - 1） < br > • 分页查询是数据库的方言， ， < br > • 如果查询的是第一页数据，起始索引可以省略，直接简写为 limit 10。< / p >
< / blockquote >
< figure class = "highlight sql" > < table > < tr > < td class = "gutter" > < pre > < span class = "line" > 1< / span > < br > < span class = "line" > 2< / span > < br > < span class = "line" > 3< / span > < br > < span class = "line" > 4< / span > < br > < span class = "line" > 5< / span > < br > < span class = "line" > 6< / span > < br > < / pre > < / td > < td class = "code" > < pre > < span class = "line" > < span class = "comment" > -- 分页查询< / span > < / span > < br > < span class = "line" > < span class = "comment" > -- 查询第一页的员工数据， < / span > < / span > < br > < span class = "line" > < span class = "keyword" > select< / span > < span class = "operator" > *< / span > < span class = "keyword" > from< / span > emp limit < span class = "number" > 0< / span > ,< span class = "number" > 10< / span > ;< / span > < br > < span class = "line" > < / span > < br > < span class = "line" > < span class = "comment" > -- 查询第二页数据，每页展示十条数据(起始索引 = （查询页码 - 1） < / span > < / span > < br > < span class = "line" > < span class = "keyword" > select< / span > < span class = "operator" > *< / span > < span class = "keyword" > from< / span > emp limit < span class = "number" > 10< / span > ,< span class = "number" > 10< / span > ;< / span > < br > < / pre > < / td > < / tr > < / table > < / figure >
< h4 id = "1-5-7-DQL语句案例" > < a href = "#1-5-7-DQL语句案例" class = "headerlink" title = "1.5.7 DQL语句案例" > < / a > 1.5.7 DQL语句案例< / h4 > < figure class = "highlight sql" > < table > < tr > < td class = "gutter" > < pre > < span class = "line" > 1< / span > < br > < span class = "line" > 2< / span > < br > < span class = "line" > 3< / span > < br > < span class = "line" > 4< / span > < br > < span class = "line" > 5< / span > < br > < span class = "line" > 6< / span > < br > < span class = "line" > 7< / span > < br > < span class = "line" > 8< / span > < br > < span class = "line" > 9< / span > < br > < span class = "line" > 10< / span > < br > < span class = "line" > 11< / span > < br > < span class = "line" > 12< / span > < br > < span class = "line" > 13< / span > < br > < span class = "line" > 14< / span > < br > < span class = "line" > 15< / span > < br > < / pre > < / td > < td class = "code" > < pre > < span class = "line" > < span class = "comment" > -- DQL语句案例< / span > < / span > < br > < span class = "line" > < span class = "comment" > -- 查询年龄在20,21,22,23岁的女性员工的信息< / span > < / span > < br > < span class = "line" > < span class = "keyword" > select< / span > < span class = "operator" > *< / span > < span class = "keyword" > from< / span > emp < span class = "keyword" > where< / span > gender < span class = "operator" > =< / span > < span class = "string" > ' 女' < / span > < span class = "keyword" > and< / span > age < span class = "keyword" > in< / span > (< span class = "number" > 20< / span > ,< span class = "number" > 21< / span > ,< span class = "number" > 22< / span > ,< span class = "number" > 23< / span > );< / span > < br > < span class = "line" > < / span > < br > < span class = "line" > < span class = "comment" > -- 查询性别为男， < / span > < / span > < br > < span class = "line" > < span class = "keyword" > select< / span > < span class = "operator" > *< / span > < span class = "keyword" > from< / span > emp < span class = "keyword" > where< / span > gender < span class = "operator" > =< / span > < span class = "string" > ' 男' < / span > < span class = "keyword" > and< / span > (age < span class = "keyword" > between< / span > < span class = "number" > 20< / span > < span class = "keyword" > and< / span > < span class = "number" > 40< / span > ) < span class = "keyword" > and< / span > name < span class = "keyword" > like< / span > < span class = "string" > ' ___' < / span > ;< / span > < br > < span class = "line" > < / span > < br > < span class = "line" > < span class = "comment" > -- 统计员工表中， ， < / span > < / span > < br > < span class = "line" > < span class = "keyword" > select< / span > gender,< span class = "built_in" > count< / span > (< span class = "operator" > *< / span > ) < span class = "keyword" > from< / span > emp < span class = "keyword" > where< / span > age < span class = "operator" > < < / span > < span class = "number" > 60< / span > < span class = "keyword" > group< / span > < span class = "keyword" > by< / span > gender;< / span > < br > < span class = "line" > < / span > < br > < span class = "line" > < span class = "comment" > -- 查询所有年龄小于等于35岁员工的姓名和年龄， ， < / span > < / span > < br > < span class = "line" > < span class = "keyword" > select< / span > name,age < span class = "keyword" > from< / span > emp < span class = "keyword" > where< / span > age < span class = "operator" > < =< / span > < span class = "number" > 35< / span > < span class = "keyword" > order< / span > < span class = "keyword" > by< / span > age < span class = "keyword" > asc< / span > ,entrydate < span class = "keyword" > desc< / span > ;< / span > < br > < span class = "line" > < / span > < br > < span class = "line" > < span class = "comment" > -- 查询性别为男,且年龄在20·40岁(含)以内的前五个员工信息，并对查询结果按年龄升序排序，如果年龄相同按照入职时间升序排序< / span > < / span > < br > < span class = "line" > < span class = "keyword" > select< / span > < span class = "operator" > *< / span > < span class = "keyword" > from< / span > emp < span class = "keyword" > where< / span > gender < span class = "operator" > =< / span > < span class = "string" > ' 男' < / span > < span class = "keyword" > and< / span > age < span class = "keyword" > between< / span > < span class = "number" > 20< / span > < span class = "keyword" > and< / span > < span class = "number" > 40< / span > < span class = "keyword" > order< / span > < span class = "keyword" > by< / span > age,entrydate limit < span class = "number" > 5< / span > ;< / span > < br > < / pre > < / td > < / tr > < / table > < / figure >
< h4 id = "1-5-8-执行顺序" > < a href = "#1-5-8-执行顺序" class = "headerlink" title = "1.5.8 执行顺序" > < / a > 1.5.8 执行顺序< / h4 > < p > < img src = "/pictures/image-20231001171425562.png" alt = "image-20231001171425562" > < / p >
< p > < img src = "/pictures/image-20231001172032063.png" alt = "image-20231001172032063" > < / p >
< p > < strong > 总结< / strong > < / p >
< p > < img src = "/pictures/image-20231001172211635.png" alt = "image-20231001172211635" > < / p >
< h3 id = "1-6-DCL-数据控制语言" > < a href = "#1-6-DCL-数据控制语言" class = "headerlink" title = "1.6 DCL-数据控制语言" > < / a > 1.6 DCL-数据控制语言< / h3 > < h4 id = "1-6-1-管理用户" > < a href = "#1-6-1-管理用户" class = "headerlink" title = "1.6.1 管理用户" > < / a > 1.6.1 管理用户< / h4 > < p > 查询用户: < code > select * from mysql.user;< / code > < / p >
< p > 创建用户:< code > CREATE USER ' 用户名' @' 主机名' IDENTIFIED BY ' 密码' ;< / code > < / p >
< p > 修改用户密码: < code > ALTER USER ' 用户名' @' 主机名' IDENTIFIED WITH mysql_native_password BY ' 新密码' ;< / code > < / p >
< p > 删除用户:< code > DROP USER ' 用户名' @' 主机名' ;< / code > < / p >
< p > < img src = "/pictures/image-20231001172731731.png" alt = "image-20231001172731731" > < / p >
< blockquote >
< p > 注意事项:< br > • 在MySQL中需要通过用户名@主机名的方式，来唯一标识一个用户< / p >
< p > • 主机名可以使用 % 通配< / p >
< p > • 这类SQL开发人员操作的比较少， （ < / p >
< /blockquote>
< figure class = "highlight sql" > < table > < tr > < td class = "gutter" > < pre > < span class = "line" > 1< / span > < br > < span class = "line" > 2< / span > < br > < span class = "line" > 3< / span > < br > < span class = "line" > 4< / span > < br > < span class = "line" > 5< / span > < br > < span class = "line" > 6< / span > < br > < span class = "line" > 7< / span > < br > < span class = "line" > 8< / span > < br > < span class = "line" > 9< / span > < br > < span class = "line" > 10< / span > < br > < span class = "line" > 11< / span > < br > < span class = "line" > 12< / span > < br > < span class = "line" > 13< / span > < br > < span class = "line" > 14< / span > < br > < span class = "line" > 15< / span > < br > < span class = "line" > 16< / span > < br > < span class = "line" > 17< / span > < br > < / pre > < / td > < td class = "code" > < pre > < span class = "line" > < span class = "comment" > -- 切换到系统中自带的mysql数据库< / span > < / span > < br > < span class = "line" > use mysql;< / span > < br > < span class = "line" > < / span > < br > < span class = "line" > < span class = "comment" > -- 查询所有的用户< / span > < / span > < br > < span class = "line" > < span class = "keyword" > select< / span > < span class = "operator" > *< / span > < span class = "keyword" > from< / span > mysql.user;< / span > < br > < span class = "line" > < / span > < br > < span class = "line" > < span class = "comment" > -- 创建用户itcast, 只能够在当前主机localhost访问, 密码123456;< / span > < / span > < br > < span class = "line" > < span class = "keyword" > create< / span > < span class = "keyword" > user< / span > < span class = "string" > ' itcast' < / span > @< span class = "string" > ' localhost' < / span > identified < span class = "keyword" > by< / span > < span class = "string" > ' 123456' < / span > ;< / span > < br > < span class = "line" > < / span > < br > < span class = "line" > < span class = "comment" > -- 创建用户heima, 可以在任意主机访问该数据库, 密码123456;< / span > < / span > < br > < span class = "line" > < span class = "keyword" > create< / span > < span class = "keyword" > user< / span > < span class = "string" > ' heima' < / span > @< span class = "string" > ' %' < / span > identified < span class = "keyword" > by< / span > < span class = "string" > ' 123456' < / span > ;< / span > < br > < span class = "line" > < / span > < br > < span class = "line" > < span class = "comment" > -- 修改用户heima的访问密码为1234;< / span > < / span > < br > < span class = "line" > < span class = "keyword" > alter< / span > < span class = "keyword" > user< / span > < span class = "string" > ' heima' < / span > @< span class = "string" > ' %' < / span > identified < span class = "keyword" > with< / span > mysql_native_password < span class = "keyword" > by< / span > < span class = "string" > ' 1234' < / span > ;< / span > < br > < span class = "line" > < / span > < br > < span class = "line" > < span class = "comment" > -- 删除 itcast@localhost 用户< / span > < / span > < br > < span class = "line" > < span class = "keyword" > drop< / span > < span class = "keyword" > user< / span > < span class = "string" > ' itcast' < / span > @< span class = "string" > ' localhost' < / span > ;< / span > < br > < / pre > < / td > < / tr > < / table > < / figure >
< h4 id = "1-6-2-权限控制" > < a href = "#1-6-2-权限控制" class = "headerlink" title = "1.6.2 权限控制" > < / a > 1.6.2 权限控制< / h4 > < p > 查询权限: < code > SHOW GRANTS FOR ' 用户名' @' 主机名' ;< / code > < / p >
< p > 授予权限: < code > GRANT 权限列表 ON 数据库名.表名 TO ' 用户名' @' 主机名' ;< / code > < / p >
< p > 撤销权限: < code > REVOKE 权限列表 ON 数据库名.表名 FROM ' 用户名' @' 主机名' ;< / code > < / p >
< blockquote >
< p > 注意事项：< br > • 多个权限之间，使用逗号分隔< br > • 授权时， 数据库名和表名可以使用 * 进行通配，代表所有< / p >
< / blockquote >
< p > < img src = "/pictures/image-20231001174406029.png" alt = "image-20231001174406029" > < / p >
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< figure class = "highlight sql" > < table > < tr > < td class = "gutter" > < pre > < span class = "line" > 1< / span > < br > < span class = "line" > 2< / span > < br > < span class = "line" > 3< / span > < br > < span class = "line" > 4< / span > < br > < span class = "line" > 5< / span > < br > < span class = "line" > 6< / span > < br > < span class = "line" > 7< / span > < br > < span class = "line" > 8< / span > < br > < span class = "line" > 9< / span > < br > < span class = "line" > 10< / span > < br > < span class = "line" > 11< / span > < br > < span class = "line" > 12< / span > < br > < / pre > < / td > < td class = "code" > < pre > < span class = "line" > < span class = "comment" > -- 权限控制< / span > < / span > < br > < span class = "line" > < span class = "comment" > -- 查询权限(查询heima用户的所有权限)< / span > < / span > < br > < span class = "line" > < span class = "keyword" > show< / span > grants < span class = "keyword" > for< / span > < span class = "string" > ' heima' < / span > @< span class = "string" > ' %' < / span > ;< / span > < br > < span class = "line" > < / span > < br > < span class = "line" > < span class = "comment" > -- 授予权限(授予heima用户对数据库itcast的所有权限)< / span > < / span > < br > < span class = "line" > < span class = "keyword" > grant< / span > < span class = "keyword" > all< / span > < span class = "keyword" > on< / span > itcast.< span class = "operator" > *< / span > < span class = "keyword" > to< / span > < span class = "string" > ' heima' < / span > @< span class = "string" > ' %' < / span > ;< / span > < br > < span class = "line" > < / span > < br > < span class = "line" > < span class = "comment" > -- 授予用户所有数据库所有表的所有权限(相当于超级管理员)< / span > < / span > < br > < span class = "line" > < span class = "keyword" > grant< / span > < span class = "keyword" > all< / span > < span class = "keyword" > on< / span > < span class = "operator" > *< / span > .< span class = "operator" > *< / span > < span class = "keyword" > to< / span > < span class = "string" > ' heima' < / span > @< span class = "string" > ' %' < / span > ;< / span > < br > < span class = "line" > < / span > < br > < span class = "line" > < span class = "comment" > -- 撤销权限(撤销heima用户在itcast数据库上的所有权限)< / span > < / span > < br > < span class = "line" > < span class = "keyword" > revoke< / span > < span class = "keyword" > all< / span > < span class = "keyword" > on< / span > itcast.< span class = "operator" > *< / span > < span class = "keyword" > from< / span > < span class = "string" > ' heima' < / span > @< span class = "string" > ' %' < / span > ;< / span > < br > < / pre > < / td > < / tr > < / table > < / figure >
< p > < strong > 总结< / strong > < / p >
< p > < img src = "/pictures/image-20231001213059144.png" alt = "image-20231001213059144" > < / p >
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< p > < strong > 全部的SQL< / strong > < / p >
< figure class = "highlight sql" > < table > < tr > < td class = "gutter" > < pre > < span class = "line" > 1< / span > < br > < span class = "line" > 2< / span > < br > < span class = "line" > 3< / span > < br > < span class = "line" > 4< / span > < br > < span class = "line" > 5< / span > < br > < span class = "line" > 6< / span > < br > < span class = "line" > 7< / span > < br > < span class = "line" > 8< / span > < br > < span class = "line" > 9< / span > < br > < span class = "line" > 10< / span > < br > < span class = "line" > 11< / span > < br > < span class = "line" > 12< / span > < br > < span class = "line" > 13< / span > < br > < span class = "line" > 14< / span > < br > < span class = "line" > 15< / span > < br > < span class = "line" > 16< / span > < br > < span class = "line" > 17< / span > < br > < span class = "line" > 18< / span > < br > < span class = "line" > 19< / span > < br > < span class = "line" > 20< / span > < br > < span class = "line" > 21< / span > < br > < span class = "line" > 22< / span > < br > < span class = "line" > 23< / span > < br > < span class = "line" > 24< / span > < br > < span class = "line" > 25< / span > < br > < span class = "line" > 26< / span > < br > < span class = "line" > 27< / span > < br > < span class = "line" > 28< / span > < br > < span class = "line" > 29< / span > < br > < span class = "line" > 30< / span > < br > < span class = "line" > 31< / span > < br > < span class = "line" > 32< / span > < br > < span class = "line" > 33< / span > < br > < span class = "line" > 34< / span > < br > < span class = "line" > 35< / span > < br > < span class = "line" > 36< / span > < br > < span class = "line" > 37< / span > < br > < span class = "line" > 38< / span > < br > < span class = "line" > 39< / span > < br > < span class = "line" > 40< / span > < br > < span class = "line" > 41< / span > < br > < span class = "line" > 42< / span > < br > < span class = "line" > 43< / span > < br > < span class = "line" > 44< / span > < br > < span class = "line" > 45< / span > < br > < span class = "line" > 46< / span > < br > < span class = "line" > 47< / span > < br > < span class = "line" > 48< / span > < br > < span class = "line" > 49< / span > < br > < span class = "line" > 50< / span > < br > < span class = "line" > 51< / span > < br > < span class = "line" > 52< / span > < br > < span class = "line" > 53< / span > < br > < span class = "line" > 54< / span > < br > < span class = "line" > 55< / span > < br > < span class = "line" > 56< / span > < br > < span class = "line" > 57< / span > < br > < span class = "line" > 58< / span > < br > < span class = "line" > 59< / span > < br > < span class = "line" > 60< / span > < br > < span class = "line" > 61< / span > < br > < span class = "line" > 62< / span > < br > < span class = "line" > 63< / span > < br > < span class = "line" > 64< / span > < br > < span class = "line" > 65< / span > < br > < span class = "line" > 66< / span > < br > < span class = "line" > 67< / span > < br > < span class = "line" > 68< / span > < br > < span class = "line" > 69< / span > < br > < span class = "line" > 70< / span > < br > < span class = "line" > 71< / span > < br > < span class = "line" > 72< / span > < br > < span class = "line" > 73< / span > < br > < span class = "line" > 74< / span > < br > < span class = "line" > 75< / span > < br > < span class = "line" > 76< / span > < br > < span class = "line" > 77< / span > < br > < span class = "line" > 78< / span > < br > < span class = "line" > 79< / span > < br > < span class = "line" > 80< / span > < br > < span class = "line" > 81< / span > < br > < span class = "line" > 82< / span > < br > < span class = "line" > 83< / span > < br > < span class = "line" > 84< / span > < br > < span class = "line" > 85< / span > < br > < span class = "line" > 86< / span > < br > < span class = "line" > 87< / span > < br > < span class = "line" > 88< / span > < br > < span class = "line" > 89< / span > < br > < span class = "line" > 90< / span > < br > < span class = "line" > 91< / span > < br > < span class = "line" > 92< / span > < br > < span class = "line" > 93< / span > < br > < span class = "line" > 94< / span > < br > < span class = "line" > 95< / span > < br > < span class = "line" > 96< / span > < br > < span class = "line" > 97< / span > < br > < span class = "line" > 98< / span > < br > < span class = "line" > 99< / span > < br > < span class = "line" > 100< / span > < br > < span class = "line" > 101< / span > < br > < span class = "line" > 102< / span > < br > < span class = "line" > 103< / span > < br > < span class = "line" > 104< / span > < br > < span class = "line" > 105< / span > < br > < span class = "line" > 106< / span > < br > < span class = "line" > 107< / span > < br > < span class = "line" > 108< / span > < br > < span class = "line" > 109< / span > < br > < span class = "line" > 110< / span > < br > < span class = "line" > 111< / span > < br > < span class = "line" > 112< / span > < br > < span class = "line" > 113< / span > < br > < span class = "line" > 114< / span > < br > < span class = "line" > 115< / span > < br > < span class = "line" > 116< / span > < br > < span class = "line" > 117< / span > < br > < span class = "line" > 118< / span > < br > < span class = "line" > 119< / span > < br > < span class = "line" > 120< / span > < br > < span class = "line" > 121< / span > < br > < span class = "line" > 122< / span > < br > < span class = "line" > 123< / span > < br > < span class = "line" > 124< / span > < br > < span class = "line" > 125< / span > < br > < span class = "
2023-10-01 22:12:48 +08:00
< h2 id = "2-函数" > < a href = "#2-函数" class = "headerlink" title = "2.函数" > < / a > 2.函数< / h2 > < h3 id = "2-1-字符串函数" > < a href = "#2-1-字符串函数" class = "headerlink" title = "2.1 字符串函数" > < / a > 2.1 字符串函数< / h3 > < p > < img src = "/pictures/image-20231001213558221.png" alt = "image-20231001213558221" > < / p >
< figure class = "highlight sql" > < table > < tr > < td class = "gutter" > < pre > < span class = "line" > 1< / span > < br > < span class = "line" > 2< / span > < br > < span class = "line" > 3< / span > < br > < span class = "line" > 4< / span > < br > < span class = "line" > 5< / span > < br > < span class = "line" > 6< / span > < br > < span class = "line" > 7< / span > < br > < span class = "line" > 8< / span > < br > < span class = "line" > 9< / span > < br > < span class = "line" > 10< / span > < br > < span class = "line" > 11< / span > < br > < span class = "line" > 12< / span > < br > < span class = "line" > 13< / span > < br > < span class = "line" > 14< / span > < br > < span class = "line" > 15< / span > < br > < span class = "line" > 16< / span > < br > < span class = "line" > 17< / span > < br > < span class = "line" > 18< / span > < br > < span class = "line" > 19< / span > < br > < span class = "line" > 20< / span > < br > < / pre > < / td > < td class = "code" > < pre > < span class = "line" > < span class = "comment" > -- concat函数(字符串拼接)< / span > < / span > < br > < span class = "line" > < span class = "keyword" > select< / span > concat(< span class = "string" > ' hello ' < / span > ,< span class = "string" > ' word' < / span > ); # hello word< / span > < br > < span class = "line" > < / span > < br > < span class = "line" > < span class = "comment" > -- lower(全部转化成小写)< / span > < / span > < br > < span class = "line" > < span class = "keyword" > select< / span > < span class = "built_in" > lower< / span > (< span class = "string" > ' Hello' < / span > ); # hello< / span > < br > < span class = "line" > < / span > < br > < span class = "line" > < span class = "comment" > -- upper(全部转化成大写)< / span > < / span > < br > < span class = "line" > < span class = "keyword" > select< / span > < span class = "built_in" > upper< / span > (< span class = "string" > ' Hello' < / span > ); # HELLO< / span > < br > < span class = "line" > < / span > < br > < span class = "line" > < span class = "comment" > -- lpad(左侧填充)< / span > < / span > < br > < span class = "line" > < span class = "keyword" > select< / span > lpad(< span class = "string" > ' 01' < / span > ,< span class = "number" > 5< / span > ,< span class = "string" > ' -' < / span > ); # < span class = "comment" > ---01< / span > < / span > < br > < span class = "line" > < / span > < br > < span class = "line" > < span class = "comment" > -- rpad(右侧填充)< / span > < / span > < br > < span class = "line" > < span class = "keyword" > select< / span > rpad(< span class = "string" > ' 01' < / span > ,< span class = "number" > 5< / span > ,< span class = "string" > ' -' < / span > ) ;# < span class = "number" > 01< / span > < span class = "comment" > ---< / span > < / span > < br > < span class = "line" > < / span > < br > < span class = "line" > < span class = "comment" > -- trim 去除头部和尾部的空格< / span > < / span > < br > < span class = "line" > < span class = "keyword" > select< / span > < span class = "built_in" > trim< / span > (< span class = "string" > ' Hello Mysql ' < / span > );# Hello Mysql< / span > < br > < span class = "line" > < / span > < br > < span class = "line" > < span class = "comment" > -- substring 字符串截取< / span > < / span > < br > < span class = "line" > < span class = "keyword" > select< / span > < span class = "built_in" > substring< / span > (< span class = "string" > ' Hello Mysql' < / span > ,< span class = "number" > 1< / span > ,< span class = "number" > 5< / span > );# Hello< / span > < br > < / pre > < / td > < / tr > < / table > < / figure >
< p > < strong > 案例< / strong > < / p >
< figure class = "highlight sql" > < table > < tr > < td class = "gutter" > < pre > < span class = "line" > 1< / span > < br > < span class = "line" > 2< / span > < br > < / pre > < / td > < td class = "code" > < pre > < span class = "line" > < span class = "comment" > -- 由于业务需求变更， ， ， < / span > < / span > < br > < span class = "line" > < span class = "keyword" > update< / span > emp < span class = "keyword" > set< / span > workno < span class = "operator" > =< / span > lpad(workno,< span class = "number" > 5< / span > ,< span class = "string" > ' 0' < / span > );< / span > < br > < / pre > < / td > < / tr > < / table > < / figure >
< h3 id = "2-2-数值函数" > < a href = "#2-2-数值函数" class = "headerlink" title = "2.2 数值函数" > < / a > 2.2 数值函数< / h3 > < p > < img src = "/pictures/image-20231001215546554.png" alt = "image-20231001215546554" > < / p >
< figure class = "highlight sql" > < table > < tr > < td class = "gutter" > < pre > < span class = "line" > 1< / span > < br > < span class = "line" > 2< / span > < br > < span class = "line" > 3< / span > < br > < span class = "line" > 4< / span > < br > < span class = "line" > 5< / span > < br > < span class = "line" > 6< / span > < br > < span class = "line" > 7< / span > < br > < span class = "line" > 8< / span > < br > < span class = "line" > 9< / span > < br > < span class = "line" > 10< / span > < br > < span class = "line" > 11< / span > < br > < span class = "line" > 12< / span > < br > < span class = "line" > 13< / span > < br > < span class = "line" > 14< / span > < br > < span class = "line" > 15< / span > < br > < / pre > < / td > < td class = "code" > < pre > < span class = "line" > < span class = "comment" > -- 数值函数< / span > < / span > < br > < span class = "line" > < span class = "comment" > -- ceil 向上取整< / span > < / span > < br > < span class = "line" > < span class = "keyword" > select< / span > < span class = "built_in" > ceil< / span > (< span class = "number" > 1.5< / span > ); # < span class = "number" > 2< / span > < / span > < br > < span class = "line" > < / span > < br > < span class = "line" > < span class = "comment" > -- floor 向下取整< / span > < / span > < br > < span class = "line" > < span class = "keyword" > select< / span > < span class = "built_in" > floor< / span > (< span class = "number" > 1.1< / span > ); # < span class = "number" > 1< / span > < / span > < br > < span class = "line" > < / span > < br > < span class = "line" > < span class = "comment" > -- mod 求模运算< / span > < / span > < br > < span class = "line" > < span class = "keyword" > select< / span > < span class = "built_in" > mod< / span > (< span class = "number" > 7< / span > ,< span class = "number" > 4< / span > ); # < span class = "number" > 3< / span > < / span > < br > < span class = "line" > < / span > < br > < span class = "line" > < span class = "comment" > -- rand 随机数(0~1)< / span > < / span > < br > < span class = "line" > < span class = "keyword" > select< / span > rand();< / span > < br > < span class = "line" > < / span > < br > < span class = "line" > < span class = "comment" > -- round 四舍五入< / span > < / span > < br > < span class = "line" > < span class = "keyword" > select< / span > round(< span class = "number" > 2.345< / span > ,< span class = "number" > 2< / span > ); # < span class = "number" > 2.35< / span > < / span > < br > < / pre > < / td > < / tr > < / table > < / figure >
< p > < strong > 案例< / strong > < / p >
< figure class = "highlight sql" > < table > < tr > < td class = "gutter" > < pre > < span class = "line" > 1< / span > < br > < span class = "line" > 2< / span > < br > < span class = "line" > 3< / span > < br > < span class = "line" > 4< / span > < br > < / pre > < / td > < td class = "code" > < pre > < span class = "line" > < span class = "comment" > -- 通过数据库函数生成一个的随机的六位验证码< / span > < / span > < br > < span class = "line" > < span class = "comment" > -- 思路是通过rand()*100生成xxxxxx.xxx的小数,然后通过round四舍五入掉小数位， ， < / span > < / span > < br > < span class = "line" > < span class = "comment" > -- 通过lpd函数补齐六位< / span > < / span > < br > < span class = "line" > < span class = "keyword" > select< / span > lpad(round(rand()< span class = "operator" > *< / span > < span class = "number" > 1000000< / span > ,< span class = "number" > 0< / span > ),< span class = "number" > 6< / span > ,< span class = "string" > ' 0' < / span > );< / span > < br > < / pre > < / td > < / tr > < / table > < / figure >
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< h3 id = "2-3-日期函数" > < a href = "#2-3-日期函数" class = "headerlink" title = "2.3 日期函数" > < / a > 2.3 日期函数< / h3 > < p > < img src = "/pictures/image-20231002114046980.png" alt = "image-20231002114046980" > < / p >
< figure class = "highlight sql" > < table > < tr > < td class = "gutter" > < pre > < span class = "line" > 1< / span > < br > < span class = "line" > 2< / span > < br > < span class = "line" > 3< / span > < br > < span class = "line" > 4< / span > < br > < span class = "line" > 5< / span > < br > < span class = "line" > 6< / span > < br > < span class = "line" > 7< / span > < br > < span class = "line" > 8< / span > < br > < span class = "line" > 9< / span > < br > < span class = "line" > 10< / span > < br > < span class = "line" > 11< / span > < br > < span class = "line" > 12< / span > < br > < span class = "line" > 13< / span > < br > < span class = "line" > 14< / span > < br > < span class = "line" > 15< / span > < br > < span class = "line" > 16< / span > < br > < span class = "line" > 17< / span > < br > < span class = "line" > 18< / span > < br > < span class = "line" > 19< / span > < br > < span class = "line" > 20< / span > < br > < span class = "line" > 21< / span > < br > < / pre > < / td > < td class = "code" > < pre > < span class = "line" > < span class = "comment" > -- 日期函数< / span > < / span > < br > < span class = "line" > < span class = "comment" > -- curdate： < / span > < / span > < br > < span class = "line" > < span class = "keyword" > select< / span > curdate();< / span > < br > < span class = "line" > < / span > < br > < span class = "line" > < span class = "comment" > -- curtime： < / span > < / span > < br > < span class = "line" > < span class = "keyword" > select< / span > curtime();< / span > < br > < span class = "line" > < / span > < br > < span class = "line" > < span class = "comment" > -- now： < / span > < / span > < br > < span class = "line" > < span class = "keyword" > select< / span > now();< / span > < br > < span class = "line" > < / span > < br > < span class = "line" > < span class = "comment" > -- YEAR , MONTH , DAY： < / span > < / span > < br > < span class = "line" > < span class = "keyword" > select< / span > < span class = "keyword" > year< / span > (now());< / span > < br > < span class = "line" > < span class = "keyword" > select< / span > < span class = "keyword" > month< / span > (now());< / span > < br > < span class = "line" > < span class = "keyword" > select< / span > < span class = "keyword" > day< / span > (now());< / span > < br > < span class = "line" > < / span > < br > < span class = "line" > < span class = "comment" > -- date_add： < / span > < / span > < br > < span class = "line" > < span class = "keyword" > select< / span > date_add(now(),< span class = "type" > INTERVAL< / span > < span class = "number" > 70< / span > < span class = "keyword" > DAY< / span > ); # 当前的时间往后推< span class = "number" > 70< / span > 天< / span > < br > < span class = "line" > < span class = "keyword" > select< / span > date_add(now(),< span class = "type" > INTERVAL< / span > < span class = "number" > 2< / span > < span class = "keyword" > MONTH< / span > ); #向后推< span class = "number" > 2< / span > 个月< / span > < br > < span class = "line" > < / span > < br > < span class = "line" > < span class = "comment" > -- datediff： < / span > < / span > < br > < span class = "line" > < span class = "keyword" > select< / span > datediff(< span class = "string" > ' 2021-12-01' < / span > ,< span class = "string" > ' 2021-10-01' < / span > ); # 查询两个时间之间的差值，第一个时间减去第二个时间< / span > < br > < / pre > < / td > < / tr > < / table > < / figure >
< p > < strong > 案例< / strong > < / p >
< figure class = "highlight sql" > < table > < tr > < td class = "gutter" > < pre > < span class = "line" > 1< / span > < br > < span class = "line" > 2< / span > < br > < / pre > < / td > < td class = "code" > < pre > < span class = "line" > < span class = "comment" > -- 查询所有员工的入职天数，并根据入职天数倒叙排序< / span > < / span > < br > < span class = "line" > < span class = "keyword" > select< / span > name,datediff(curdate(),entrydate) < span class = "string" > ' entrydays' < / span > < span class = "keyword" > from< / span > emp < span class = "keyword" > order< / span > < span class = "keyword" > by< / span > entrydays < span class = "keyword" > desc< / span > ;< / span > < br > < / pre > < / td > < / tr > < / table > < / figure >
< h3 id = "2-4-流程函数" > < a href = "#2-4-流程函数" class = "headerlink" title = "2.4 流程函数" > < / a > 2.4 流程函数< / h3 > < p > < img src = "/pictures/image-20231004124942068.png" alt = "image-20231004124942068" > < / p >
< figure class = "highlight sql" > < table > < tr > < td class = "gutter" > < pre > < span class = "line" > 1< / span > < br > < span class = "line" > 2< / span > < br > < span class = "line" > 3< / span > < br > < span class = "line" > 4< / span > < br > < span class = "line" > 5< / span > < br > < span class = "line" > 6< / span > < br > < span class = "line" > 7< / span > < br > < span class = "line" > 8< / span > < br > < span class = "line" > 9< / span > < br > < span class = "line" > 10< / span > < br > < span class = "line" > 11< / span > < br > < span class = "line" > 12< / span > < br > < span class = "line" > 13< / span > < br > < span class = "line" > 14< / span > < br > < span class = "line" > 15< / span > < br > < span class = "line" > 16< / span > < br > < span class = "line" > 17< / span > < br > < / pre > < / td > < td class = "code" > < pre > < span class = "line" > < span class = "comment" > -- 流程控制函数< / span > < / span > < br > < span class = "line" > < span class = "comment" > -- if 相当java中的三元运算符< / span > < / span > < br > < span class = "line" > < span class = "keyword" > select< / span > if(< span class = "literal" > true< / span > , < span class = "string" > ' OK' < / span > , < span class = "string" > ' ERROR' < / span > );< / span > < br > < span class = "line" > < / span > < br > < span class = "line" > < span class = "comment" > -- ifnull 第一个字符串不为空就返回第一个，第一个为空就返回第二个< / span > < / span > < br > < span class = "line" > < span class = "keyword" > select< / span > ifnull(< span class = "string" > ' OK' < / span > , < span class = "string" > ' DEFAULT' < / span > );< / span > < br > < span class = "line" > < span class = "keyword" > select< / span > ifnull(< span class = "keyword" > null< / span > , < span class = "string" > ' DEFAULT' < / span > );< / span > < br > < span class = "line" > < / span > < br > < span class = "line" > < span class = "comment" > -- case when then else end< / span > < / span > < br > < span class = "line" > < span class = "comment" > -- 需求: 查询emp表的员工姓名和工作地址 (北京/上海 ----> 一线城市 , 其他 ----> 二线城市)< / span > < / span > < br > < span class = "line" > < span class = "keyword" > select< / span > name,< / span > < br > < span class = "line" > (< span class = "keyword" > case< / span > workaddress< / span > < br > < span class = "line" > < span class = "keyword" > when< / span > < span class = "string" > ' 北京' < / span > < span class = "keyword" > then< / span > < span class = "string" > ' 一线城市' < / span > < / span > < br > < span class = "line" > < span class = "keyword" > when< / span > < span class = "string" > ' 上海' < / span > < span class = "keyword" > then< / span > < span class = "string" > ' 一线城市' < / span > < / span > < br > < span class = "line" > < span class = "keyword" > else< / span > < / span > < br > < span class = "line" > < span class = "string" > ' 二线城市' < / span > < span class = "keyword" > end< / span > ) < span class = "keyword" > as< / span > < span class = "string" > ' 工作地址' < / span > < / span > < br > < span class = "line" > < span class = "keyword" > from< / span > emp;< / span > < br > < / pre > < / td > < / tr > < / table > < / figure >
< p > < strong > 案例< / strong > < / p >
< figure class = "highlight sql" > < table > < tr > < td class = "gutter" > < pre > < span class = "line" > 1< / span > < br > < span class = "line" > 2< / span > < br > < span class = "line" > 3< / span > < br > < span class = "line" > 4< / span > < br > < span class = "line" > 5< / span > < br > < span class = "line" > 6< / span > < br > < span class = "line" > 7< / span > < br > < span class = "line" > 8< / span > < br > < span class = "line" > 9< / span > < br > < span class = "line" > 10< / span > < br > < span class = "line" > 11< / span > < br > < span class = "line" > 12< / span > < br > < span class = "line" > 13< / span > < br > < span class = "line" > 14< / span > < br > < span class = "line" > 15< / span > < br > < span class = "line" > 16< / span > < br > < span class = "line" > 17< / span > < br > < span class = "line" > 18< / span > < br > < span class = "line" > 19< / span > < br > < span class = "line" > 20< / span > < br > < span class = "line" > 21< / span > < br > < span class = "line" > 22< / span > < br > < span class = "line" > 23< / span > < br > < span class = "line" > 24< / span > < br > < span class = "line" > 25< / span > < br > < span class = "line" > 26< / span > < br > < span class = "line" > 27< / span > < br > < span class = "line" > 28< / span > < br > < span class = "line" > 29< / span > < br > < span class = "line" > 30< / span > < br > < span class = "line" > 31< / span > < br > < span class = "line" > 32< / span > < br > < span class = "line" > 33< / span > < br > < span class = "line" > 34< / span > < br > < span class = "line" > 35< / span > < br > < span class = "line" > 36< / span > < br > < span class = "line" > 37< / span > < br > < span class = "line" > 38< / span > < br > < / pre > < / td > < td class = "code" > < pre > < span class = "line" > < span class = "comment" > -- 案例：统计班级各个学员的成绩，展示规则如下:< / span > < / span > < br > < span class = "line" > < span class = "comment" > -- > = 85 展示优秀< / span > < / span > < br > < span class = "line" > < span class = "comment" > -- > = 60 展示及格< / span > < / span > < br > < span class = "line" > < span class = "comment" > -- 否则展示不及格< / span > < / span > < br > < span class = "line" > < / span > < br > < span class = "line" > < span class = "comment" > -- 建表数据< / span > < / span > < br > < span class = "line" > < span class = "keyword" > create< / span > < span class = "keyword" > table< / span > score< / span > < br > < span class = "line" > (< / span > < br > < span class = "line" > id < span class = "type" > int< / span > comment < span class = "string" > ' ID' < / span > ,< / span > < br > < span class = "line" > name < span class = "type" > varchar< / span > (< span class = "number" > 20< / span > ) comment < span class = "string" > ' 姓名' < / span > ,< / span > < br > < span class = "line" > math < span class = "type" > int< / span > comment < span class = "string" > ' 数学' < / span > ,< / span > < br > < span class = "line" > english < span class = "type" > int< / span > comment < span class = "string" > ' 英语' < / span > ,< / span > < br > < span class = "line" > chinese < span class = "type" > int< / span > comment < span class = "string" > ' 语文' < / span > < / span > < br > < span class = "line" > ) comment < span class = "string" > ' 学员成绩表' < / span > ;< / span > < br > < span class = "line" > < span class = "keyword" > insert< / span > < span class = "keyword" > into< / span > score(id, name, math, english, chinese)< / span > < br > < span class = "line" > < span class = "keyword" > VALUES< / span > (< span class = "number" > 1< / span > , < span class = "string" > ' Tom' < / span > , < span class = "number" > 67< / span > , < span class = "number" > 88< / span > , < span class = "number" > 95< / span > ),< / span > < br > < span class = "line" > (< span class = "number" > 2< / span > , < span class = "string" > ' Rose' < / span > , < span class = "number" > 23< / span > , < span class = "number" > 66< / span > , < span class = "number" > 90< / span > ),< / span > < br > < span class = "line" > (< span class = "number" > 3< / span > , < span class = "string" > ' Jack' < / span > , < span class = "number" > 56< / span > , < span class = "number" > 98< / span > , < span class = "number" > 76< / span > );< / span > < br > < span class = "line" > < / span > < br > < span class = "line" > < span class = "keyword" > select< / span > < span class = "operator" > *< / span > < / span > < br > < span class = "line" > < span class = "keyword" > from< / span > score;< / span > < br > < span class = "line" > < / span > < br > < span class = "line" > < span class = "comment" > -- 案例sql实现< / span > < / span > < br > < span class = "line" > < span class = "keyword" > select< / span > id,< / span > < br > < span class = "line" > name,< / span > < br > < span class = "line" > (< span class = "keyword" > case< / span > < span class = "keyword" > when< / span > math < span class = "operator" > > =< / span > < span class = "number" > 85< / span > < span class = "keyword" > then< /sp
2023-10-04 17:12:37 +08:00
< p > < strong > 函数相关的全部sql< / strong > < / p >
< figure class = "highlight sql" > < table > < tr > < td class = "gutter" > < pre > < span class = "line" > 1< / span > < br > < span class = "line" > 2< / span > < br > < span class = "line" > 3< / span > < br > < span class = "line" > 4< / span > < br > < span class = "line" > 5< / span > < br > < span class = "line" > 6< / span > < br > < span class = "line" > 7< / span > < br > < span class = "line" > 8< / span > < br > < span class = "line" > 9< / span > < br > < span class = "line" > 10< / span > < br > < span class = "line" > 11< / span > < br > < span class = "line" > 12< / span > < br > < span class = "line" > 13< / span > < br > < span class = "line" > 14< / span > < br > < span class = "line" > 15< / span > < br > < span class = "line" > 16< / span > < br > < span class = "line" > 17< / span > < br > < span class = "line" > 18< / span > < br > < span class = "line" > 19< / span > < br > < span class = "line" > 20< / span > < br > < span class = "line" > 21< / span > < br > < span class = "line" > 22< / span > < br > < span class = "line" > 23< / span > < br > < span class = "line" > 24< / span > < br > < span class = "line" > 25< / span > < br > < span class = "line" > 26< / span > < br > < span class = "line" > 27< / span > < br > < span class = "line" > 28< / span > < br > < span class = "line" > 29< / span > < br > < span class = "line" > 30< / span > < br > < span class = "line" > 31< / span > < br > < span class = "line" > 32< / span > < br > < span class = "line" > 33< / span > < br > < span class = "line" > 34< / span > < br > < span class = "line" > 35< / span > < br > < span class = "line" > 36< / span > < br > < span class = "line" > 37< / span > < br > < span class = "line" > 38< / span > < br > < span class = "line" > 39< / span > < br > < span class = "line" > 40< / span > < br > < span class = "line" > 41< / span > < br > < span class = "line" > 42< / span > < br > < span class = "line" > 43< / span > < br > < span class = "line" > 44< / span > < br > < span class = "line" > 45< / span > < br > < span class = "line" > 46< / span > < br > < span class = "line" > 47< / span > < br > < span class = "line" > 48< / span > < br > < span class = "line" > 49< / span > < br > < span class = "line" > 50< / span > < br > < span class = "line" > 51< / span > < br > < span class = "line" > 52< / span > < br > < span class = "line" > 53< / span > < br > < span class = "line" > 54< / span > < br > < span class = "line" > 55< / span > < br > < span class = "line" > 56< / span > < br > < span class = "line" > 57< / span > < br > < span class = "line" > 58< / span > < br > < span class = "line" > 59< / span > < br > < span class = "line" > 60< / span > < br > < span class = "line" > 61< / span > < br > < span class = "line" > 62< / span > < br > < span class = "line" > 63< / span > < br > < span class = "line" > 64< / span > < br > < span class = "line" > 65< / span > < br > < span class = "line" > 66< / span > < br > < span class = "line" > 67< / span > < br > < span class = "line" > 68< / span > < br > < span class = "line" > 69< / span > < br > < span class = "line" > 70< / span > < br > < span class = "line" > 71< / span > < br > < span class = "line" > 72< / span > < br > < span class = "line" > 73< / span > < br > < span class = "line" > 74< / span > < br > < span class = "line" > 75< / span > < br > < span class = "line" > 76< / span > < br > < span class = "line" > 77< / span > < br > < span class = "line" > 78< / span > < br > < span class = "line" > 79< / span > < br > < span class = "line" > 80< / span > < br > < span class = "line" > 81< / span > < br > < span class = "line" > 82< / span > < br > < span class = "line" > 83< / span > < br > < span class = "line" > 84< / span > < br > < span class = "line" > 85< / span > < br > < span class = "line" > 86< / span > < br > < span class = "line" > 87< / span > < br > < span class = "line" > 88< / span > < br > < span class = "line" > 89< / span > < br > < span class = "line" > 90< / span > < br > < span class = "line" > 91< / span > < br > < span class = "line" > 92< / span > < br > < span class = "line" > 93< / span > < br > < span class = "line" > 94< / span > < br > < span class = "line" > 95< / span > < br > < span class = "line" > 96< / span > < br > < span class = "line" > 97< / span > < br > < span class = "line" > 98< / span > < br > < span class = "line" > 99< / span > < br > < span class = "line" > 100< / span > < br > < span class = "line" > 101< / span > < br > < span class = "line" > 102< / span > < br > < span class = "line" > 103< / span > < br > < span class = "line" > 104< / span > < br > < span class = "line" > 105< / span > < br > < span class = "line" > 106< / span > < br > < span class = "line" > 107< / span > < br > < span class = "line" > 108< / span > < br > < span class = "line" > 109< / span > < br > < span class = "line" > 110< / span > < br > < span class = "line" > 111< / span > < br > < span class = "line" > 112< / span > < br > < span class = "line" > 113< / span > < br > < span class = "line" > 114< / span > < br > < span class = "line" > 115< / span > < br > < span class = "line" > 116< / span > < br > < span class = "line" > 117< / span > < br > < span class = "line" > 118< / span > < br > < span class = "line" > 119< / span > < br > < span class = "line" > 120< / span > < br > < span class = "line" > 121< / span > < br > < span class = "line" > 122< / span > < br > < span class = "line" > 123< / span > < br > < span class = "line" > 124< / span > < br > < span class = "line" > 125< / span > < br > < span class = "
< h2 id = "3-约束" > < a href = "#3-约束" class = "headerlink" title = "3.约束" > < / a > 3.约束< / h2 > < h3 id = "3-1-概述" > < a href = "#3-1-概述" class = "headerlink" title = "3.1 概述" > < / a > 3.1 概述< / h3 > < p > < strong > 概念< / strong > ：约束是作用于表中字段上的规则，用于限制存储在表中的数据。< / p >
< p > < strong > 目的< / strong > ：保证数据库中数据的正确、有效性和完整性。< / p >
< p > < strong > 分类< / strong > :< / p >
< p > < img src = "/pictures/image-20231004130826351.png" alt = "image-20231004130826351" > < / p >
< h3 id = "3-2-约束演示" > < a href = "#3-2-约束演示" class = "headerlink" title = "3.2 约束演示" > < / a > 3.2 约束演示< / h3 > < p > < strong > 案例需求： 根据需求，完成表结构的创建，需求如下：< / strong > < / p >
< p > < img src = "/pictures/image-20231004160744943.png" alt = "image-20231004160744943" > < / p >
< p > 对应的建表语句为：< / p >
< figure class = "highlight sql" > < table > < tr > < td class = "gutter" > < pre > < span class = "line" > 1< / span > < br > < span class = "line" > 2< / span > < br > < span class = "line" > 3< / span > < br > < span class = "line" > 4< / span > < br > < span class = "line" > 5< / span > < br > < span class = "line" > 6< / span > < br > < span class = "line" > 7< / span > < br > < / pre > < / td > < td class = "code" > < pre > < span class = "line" > < span class = "keyword" > create< / span > < span class = "keyword" > table< / span > tb_user(< / span > < br > < span class = "line" > id < span class = "type" > int< / span > AUTO_INCREMENT < span class = "keyword" > PRIMARY< / span > KEY COMMENT < span class = "string" > ' ID唯一标识' < / span > ,< / span > < br > < span class = "line" > name < span class = "type" > varchar< / span > (< span class = "number" > 10< / span > ) < span class = "keyword" > NOT< / span > < span class = "keyword" > NULL< / span > < span class = "keyword" > UNIQUE< / span > COMMENT < span class = "string" > ' 姓名' < / span > ,< / span > < br > < span class = "line" > age < span class = "type" > int< / span > < span class = "keyword" > check< / span > (age < span class = "operator" > > < / span > < span class = "number" > 0< / span > < span class = "operator" > & & < / span > age < span class = "operator" > < =< / span > < span class = "number" > 120< / span > ) COMMENT < span class = "string" > ' 年龄' < / span > ,< / span > < br > < span class = "line" > status < span class = "type" > char< / span > (< span class = "number" > 1< / span > ) < span class = "keyword" > default< / span > < span class = "string" > ' 1' < / span > COMMENT < span class = "string" > ' 状态' < / span > ,< / span > < br > < span class = "line" > gender < span class = "type" > char< / span > (< span class = "number" > 1< / span > ) COMMENT < span class = "string" > ' 性别' < / span > < / span > < br > < span class = "line" > );< / span > < br > < / pre > < / td > < / tr > < / table > < / figure >
< h3 id = "3-3-外键约束" > < a href = "#3-3-外键约束" class = "headerlink" title = "3.3 外键约束" > < / a > 3.3 外键约束< / h3 > < h4 id = "3-3-1-介绍" > < a href = "#3-3-1-介绍" class = "headerlink" title = "3.3.1 介绍" > < / a > 3.3.1 介绍< / h4 > < p > < img src = "/pictures/image-20231004162616775.png" alt = "image-20231004162616775" > < / p >
< h4 id = "3-3-2-语法" > < a href = "#3-3-2-语法" class = "headerlink" title = "3.3.2 语法" > < / a > 3.3.2 语法< / h4 > < p > < strong > 建立外键< / strong > : < code > ALTER TABLE 表名 ADD CONSTRAINT 外键名称 FOREIGN KEY (外键字段名) REFERENCES 主表 (主表列名) ;< / code > < / p >
< p > < strong > 删除外键< / strong > : < code > ALTER TABLE 表名 DROP FOREIGN KEY 外键名称;< / code > < / p >
< p > < img src = "/pictures/image-20231004163021062.png" alt = "image-20231004163021062" > < / p >
< p > 举例< / p >
< figure class = "highlight sql" > < table > < tr > < td class = "gutter" > < pre > < span class = "line" > 1< / span > < br > < span class = "line" > 2< / span > < br > < span class = "line" > 3< / span > < br > < span class = "line" > 4< / span > < br > < span class = "line" > 5< / span > < br > < span class = "line" > 6< / span > < br > < span class = "line" > 7< / span > < br > < span class = "line" > 8< / span > < br > < span class = "line" > 9< / span > < br > < span class = "line" > 10< / span > < br > < span class = "line" > 11< / span > < br > < span class = "line" > 12< / span > < br > < span class = "line" > 13< / span > < br > < span class = "line" > 14< / span > < br > < span class = "line" > 15< / span > < br > < span class = "line" > 16< / span > < br > < span class = "line" > 17< / span > < br > < span class = "line" > 18< / span > < br > < span class = "line" > 19< / span > < br > < span class = "line" > 20< / span > < br > < span class = "line" > 21< / span > < br > < span class = "line" > 22< / span > < br > < span class = "line" > 23< / span > < br > < span class = "line" > 24< / span > < br > < span class = "line" > 25< / span > < br > < span class = "line" > 26< / span > < br > < span class = "line" > 27< / span > < br > < span class = "line" > 28< / span > < br > < span class = "line" > 29< / span > < br > < span class = "line" > 30< / span > < br > < span class = "line" > 31< / span > < br > < span class = "line" > 32< / span > < br > < span class = "line" > 33< / span > < br > < span class = "line" > 34< / span > < br > < span class = "line" > 35< / span > < br > < span class = "line" > 36< / span > < br > < span class = "line" > 37< / span > < br > < span class = "line" > 38< / span > < br > < span class = "line" > 39< / span > < br > < span class = "line" > 40< / span > < br > < span class = "line" > 41< / span > < br > < span class = "line" > 42< / span > < br > < span class = "line" > 43< / span > < br > < span class = "line" > 44< / span > < br > < span class = "line" > 45< / span > < br > < / pre > < / td > < td class = "code" > < pre > < span class = "line" > < span class = "comment" > -- 外键约束< / span > < / span > < br > < span class = "line" > < span class = "keyword" > create< / span > < span class = "keyword" > table< / span > dept< / span > < br > < span class = "line" > (< / span > < br > < span class = "line" > id < span class = "type" > int< / span > auto_increment comment < span class = "string" > ' ID' < / span > < span class = "keyword" > primary< / span > key,< / span > < br > < span class = "line" > name < span class = "type" > varchar< / span > (< span class = "number" > 50< / span > ) < span class = "keyword" > not< / span > < span class = "keyword" > null< / span > comment < span class = "string" > ' 部门名称' < / span > < / span > < br > < span class = "line" > ) comment < span class = "string" > ' 部门表' < / span > ;< / span > < br > < span class = "line" > < / span > < br > < span class = "line" > < span class = "keyword" > INSERT< / span > < span class = "keyword" > INTO< / span > dept (id, name)< / span > < br > < span class = "line" > < span class = "keyword" > VALUES< / span > (< span class = "number" > 1< / span > , < span class = "string" > ' 研发部' < / span > ),< / span > < br > < span class = "line" > (< span class = "number" > 2< / span > , < span class = "string" > ' 市场部' < / span > ),< / span > < br > < span class = "line" > (< span class = "number" > 3< / span > , < span class = "string" > ' 财务部' < / span > ),< / span > < br > < span class = "line" > (< span class = "number" > 4< / span > , < span class = "string" > ' 销售部' < / span > ),< / span > < br > < span class = "line" > (< span class = "number" > 5< / span > , < span class = "string" > ' 总经办' < / span > );< / span > < br > < span class = "line" > < / span > < br > < span class = "line" > < span class = "keyword" > create< / span > < span class = "keyword" > table< / span > employee< / span > < br > < span class = "line" > (< / span > < br > < span class = "line" > id < span class = "type" > int< / span > auto_increment comment < span class = "string" > ' ID' < / span > < span class = "keyword" > primary< / span > key,< / span > < br > < span class = "line" > name < span class = "type" > varchar< / span > (< span class = "number" > 50< / span > ) < span class = "keyword" > not< / span > < span class = "keyword" > null< / span > comment < span class = "string" > ' 姓名' < / span > ,< / span > < br > < span class = "line" > age < span class = "type" > int< / span > comment < span class = "string" > ' 年龄' < / span > ,< / span > < br > < span class = "line" > job < span class = "type" > varchar< / span > (< span class = "number" > 20< / span > ) comment < span class = "string" > ' 职位' < / span > ,< / span > < br > < span class = "line" > salary < span class = "type" > int< / span > comment < span class = "string" > ' 薪资' < / span > ,< / span > < br > < span class = "line" > entrydate < span class = "type" > date< / span > comment < span
2024-05-10 13:32:25 +08:00
< h4 id = "3-3-3-删除-更新行为" > < a href = "#3-3-3-删除-更新行为" class = "headerlink" title = "3.3.3 删除/更新行为" > < / a > 3.3.3 删除/ 更新行为< / h4 > < p > 详细介绍见PDF文件 < a href = "https://qingling.icu/posts/50465.html" > https://qingling.icu/posts/50465.html< / a > < / p >
2023-10-04 17:12:37 +08:00
< p > < strong > 添加了外键之后，再删除父表数据时产生的约束行为，我们就称为删除/ 更新行为。具体的删除/ 更新行为有以下几种:< / strong > < / p >
< p > < img src = "/pictures/image-20231004164211535.png" alt = "image-20231004164211535" > < / p >
< p > 具体语法为:< / p >
< p > < code > ALTER TABLE 表名 ADD CONSTRAINT 外键名称 FOREIGN KEY (外键字段) REFERENCES 主表名 (主表字段名) ON UPDATE CASCADE ON DELETE CASCADE;< / code > < / p >
< p > < strong > 约束相关的sql< / strong > < / p >
< figure class = "highlight sql" > < table > < tr > < td class = "gutter" > < pre > < span class = "line" > 1< / span > < br > < span class = "line" > 2< / span > < br > < span class = "line" > 3< / span > < br > < span class = "line" > 4< / span > < br > < span class = "line" > 5< / span > < br > < span class = "line" > 6< / span > < br > < span class = "line" > 7< / span > < br > < span class = "line" > 8< / span > < br > < span class = "line" > 9< / span > < br > < span class = "line" > 10< / span > < br > < span class = "line" > 11< / span > < br > < span class = "line" > 12< / span > < br > < span class = "line" > 13< / span > < br > < span class = "line" > 14< / span > < br > < span class = "line" > 15< / span > < br > < span class = "line" > 16< / span > < br > < span class = "line" > 17< / span > < br > < span class = "line" > 18< / span > < br > < span class = "line" > 19< / span > < br > < span class = "line" > 20< / span > < br > < span class = "line" > 21< / span > < br > < span class = "line" > 22< / span > < br > < span class = "line" > 23< / span > < br > < span class = "line" > 24< / span > < br > < span class = "line" > 25< / span > < br > < span class = "line" > 26< / span > < br > < span class = "line" > 27< / span > < br > < span class = "line" > 28< / span > < br > < span class = "line" > 29< / span > < br > < span class = "line" > 30< / span > < br > < span class = "line" > 31< / span > < br > < span class = "line" > 32< / span > < br > < span class = "line" > 33< / span > < br > < span class = "line" > 34< / span > < br > < span class = "line" > 35< / span > < br > < span class = "line" > 36< / span > < br > < span class = "line" > 37< / span > < br > < span class = "line" > 38< / span > < br > < span class = "line" > 39< / span > < br > < span class = "line" > 40< / span > < br > < span class = "line" > 41< / span > < br > < span class = "line" > 42< / span > < br > < span class = "line" > 43< / span > < br > < span class = "line" > 44< / span > < br > < span class = "line" > 45< / span > < br > < span class = "line" > 46< / span > < br > < span class = "line" > 47< / span > < br > < span class = "line" > 48< / span > < br > < span class = "line" > 49< / span > < br > < span class = "line" > 50< / span > < br > < span class = "line" > 51< / span > < br > < span class = "line" > 52< / span > < br > < span class = "line" > 53< / span > < br > < span class = "line" > 54< / span > < br > < span class = "line" > 55< / span > < br > < span class = "line" > 56< / span > < br > < span class = "line" > 57< / span > < br > < span class = "line" > 58< / span > < br > < span class = "line" > 59< / span > < br > < span class = "line" > 60< / span > < br > < span class = "line" > 61< / span > < br > < span class = "line" > 62< / span > < br > < span class = "line" > 63< / span > < br > < span class = "line" > 64< / span > < br > < span class = "line" > 65< / span > < br > < span class = "line" > 66< / span > < br > < span class = "line" > 67< / span > < br > < span class = "line" > 68< / span > < br > < span class = "line" > 69< / span > < br > < span class = "line" > 70< / span > < br > < span class = "line" > 71< / span > < br > < / pre > < / td > < td class = "code" > < pre > < span class = "line" > < span class = "comment" > -- ---------------------------------------------------约束演示------------------------------------------------------------< / span > < / span > < br > < span class = "line" > < span class = "comment" > -- id 主键，并且自动增长< / span > < / span > < br > < span class = "line" > < span class = "comment" > -- name 不为空，并且唯一< / span > < / span > < br > < span class = "line" > < span class = "comment" > -- age 大于零， （ ） > 0 & & age < = 120) COMMENT ' 年龄' < / span > < / span > < br > < span class = "line" > < span class = "comment" > -- status 如果没有指定该值， < / span > < / span > < br > < span class = "line" > < span class = "comment" > -- gender 无约束< / span > < / span > < br > < span class = "line" > < span class = "keyword" > drop< / span > < span class = "keyword" > table< / span > if < span class = "keyword" > exists< / span > < span class = "keyword" > user< / span > ;< / span > < br > < span class = "line" > < span class = "keyword" > create< / span > < span class = "keyword" > table< / span > < span class = "keyword" > user< / span > < / span > < br > < span class = "line" > (< / span > < br > < span class = "line" > id < span class = "type" > int< / span > AUTO_INCREMENT < span class = "keyword" > PRIMARY< / span > KEY COMMENT < span class = "string" > ' ID唯一标识' < / span > ,< / span > < br > < span class = "line" > name < span class = "type" > varchar< / span > (< span class = "number" > 10< / span > ) < span class = "keyword" > NOT< / span > < span class = "keyword" > NULL< / span > < span class = "keyword" > UNIQUE< / span > COMMENT < span class = "string" > ' 姓名' < / span > ,< / span > < br > < span class = "line" > age < span class = "type" > int< / span > COMMENT < span class = "string" > ' 年龄' < / span > ,< / span > < br > < span class = "line" > status < span class = "type"
< h2 id = "4-多表查询" > < a href = "#4-多表查询" class = "headerlink" title = "4.多表查询" > < / a > 4.多表查询< / h2 > < h3 id = "4-1-多表关系" > < a href = "#4-1-多表关系" class = "headerlink" title = "4.1 多表关系" > < / a > 4.1 多表关系< / h3 > < p > < strong > 一对多< / strong > < / p >
< p > < img src = "/pictures/image-20231004165257714.png" alt = "image-20231004165257714" > < / p >
< p > < strong > 多对多< / strong > < / p >
< p > < img src = "/pictures/image-20231004165425089.png" alt = "image-20231004165425089" > < / p >
< p > < strong > 一对一< / strong > < / p >
< p > < img src = "/pictures/image-20231004170148951.png" alt = "image-20231004170148951" > < / p >
< figure class = "highlight sql" > < table > < tr > < td class = "gutter" > < pre > < span class = "line" > 1< / span > < br > < span class = "line" > 2< / span > < br > < span class = "line" > 3< / span > < br > < span class = "line" > 4< / span > < br > < span class = "line" > 5< / span > < br > < span class = "line" > 6< / span > < br > < span class = "line" > 7< / span > < br > < span class = "line" > 8< / span > < br > < span class = "line" > 9< / span > < br > < span class = "line" > 10< / span > < br > < span class = "line" > 11< / span > < br > < span class = "line" > 12< / span > < br > < span class = "line" > 13< / span > < br > < span class = "line" > 14< / span > < br > < span class = "line" > 15< / span > < br > < span class = "line" > 16< / span > < br > < span class = "line" > 17< / span > < br > < span class = "line" > 18< / span > < br > < span class = "line" > 19< / span > < br > < span class = "line" > 20< / span > < br > < span class = "line" > 21< / span > < br > < span class = "line" > 22< / span > < br > < span class = "line" > 23< / span > < br > < span class = "line" > 24< / span > < br > < span class = "line" > 25< / span > < br > < span class = "line" > 26< / span > < br > < span class = "line" > 27< / span > < br > < span class = "line" > 28< / span > < br > < span class = "line" > 29< / span > < br > < span class = "line" > 30< / span > < br > < span class = "line" > 31< / span > < br > < span class = "line" > 32< / span > < br > < span class = "line" > 33< / span > < br > < span class = "line" > 34< / span > < br > < span class = "line" > 35< / span > < br > < span class = "line" > 36< / span > < br > < span class = "line" > 37< / span > < br > < span class = "line" > 38< / span > < br > < span class = "line" > 39< / span > < br > < span class = "line" > 40< / span > < br > < span class = "line" > 41< / span > < br > < span class = "line" > 42< / span > < br > < span class = "line" > 43< / span > < br > < span class = "line" > 44< / span > < br > < span class = "line" > 45< / span > < br > < span class = "line" > 46< / span > < br > < span class = "line" > 47< / span > < br > < span class = "line" > 48< / span > < br > < span class = "line" > 49< / span > < br > < span class = "line" > 50< / span > < br > < span class = "line" > 51< / span > < br > < span class = "line" > 52< / span > < br > < span class = "line" > 53< / span > < br > < span class = "line" > 54< / span > < br > < span class = "line" > 55< / span > < br > < span class = "line" > 56< / span > < br > < span class = "line" > 57< / span > < br > < span class = "line" > 58< / span > < br > < span class = "line" > 59< / span > < br > < span class = "line" > 60< / span > < br > < span class = "line" > 61< / span > < br > < span class = "line" > 62< / span > < br > < span class = "line" > 63< / span > < br > < span class = "line" > 64< / span > < br > < span class = "line" > 65< / span > < br > < span class = "line" > 66< / span > < br > < span class = "line" > 67< / span > < br > < span class = "line" > 68< / span > < br > < span class = "line" > 69< / span > < br > < span class = "line" > 70< / span > < br > < span class = "line" > 71< / span > < br > < span class = "line" > 72< / span > < br > < span class = "line" > 73< / span > < br > < span class = "line" > 74< / span > < br > < span class = "line" > 75< / span > < br > < span class = "line" > 76< / span > < br > < span class = "line" > 77< / span > < br > < / pre > < / td > < td class = "code" > < pre > < span class = "line" > < span class = "comment" > -- 多表关系< / span > < / span > < br > < span class = "line" > < span class = "comment" > -- 演示多对多的关系< / span > < / span > < br > < span class = "line" > < span class = "keyword" > create< / span > < span class = "keyword" > table< / span > student< / span > < br > < span class = "line" > (< / span > < br > < span class = "line" > id < span class = "type" > int< / span > auto_increment < span class = "keyword" > primary< / span > key comment < span class = "string" > ' 主键ID' < / span > ,< / span > < br > < span class = "line" > name < span class = "type" > varchar< / span > (< span class = "number" > 10< / span > ) comment < span class = "string" > ' 姓名' < / span > ,< / span > < br > < span class = "line" > < span class = "keyword" > no< / span > < span class = "type" > varchar< / span > (< span class = "number" > 10< / span > ) comment < span class = "string" > ' 学号' < / span > < / span > < br > < span class = "line" > ) comment < span class = "string" > ' 学生表' < / span > ;< / span > < br > < span class = "line" > < / span > < br > < span class = "line" > < span class = "keyword" > insert< / span > < span class = "keyword" > into< / span > student< / span > < br > < span class = "line" > < span class = "keyword" > values< / span > (< span class = "keyword" > null< / span > , < span class = "string" > ' 黛绮丝' < / span > , < span class = "string" > ' 2000100101' < / span > ),< / span > < br > < span class = "line" > (< span class = "keyword" > null< / span > , < span class = "string" > ' 谢逊' < / span > ,< / span > < br > < span class = "line" > < span class = "string" > ' 2000100102' < / span > ),< / span > < br > < span class = "line" > (< span class = "keyword" > null< / span > , < span cla
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< h3 id = "4-2-多表查询概述" > < a href = "#4-2-多表查询概述" class = "headerlink" title = "4.2 多表查询概述" > < / a > 4.2 多表查询概述< / h3 > < h4 id = "4-2-1-数据准备" > < a href = "#4-2-1-数据准备" class = "headerlink" title = "4.2.1 数据准备" > < / a > 4.2.1 数据准备< / h4 > < figure class = "highlight sql" > < table > < tr > < td class = "gutter" > < pre > < span class = "line" > 1< / span > < br > < span class = "line" > 2< / span > < br > < span class = "line" > 3< / span > < br > < span class = "line" > 4< / span > < br > < span class = "line" > 5< / span > < br > < span class = "line" > 6< / span > < br > < span class = "line" > 7< / span > < br > < span class = "line" > 8< / span > < br > < span class = "line" > 9< / span > < br > < span class = "line" > 10< / span > < br > < span class = "line" > 11< / span > < br > < span class = "line" > 12< / span > < br > < span class = "line" > 13< / span > < br > < span class = "line" > 14< / span > < br > < span class = "line" > 15< / span > < br > < span class = "line" > 16< / span > < br > < span class = "line" > 17< / span > < br > < span class = "line" > 18< / span > < br > < span class = "line" > 19< / span > < br > < span class = "line" > 20< / span > < br > < span class = "line" > 21< / span > < br > < span class = "line" > 22< / span > < br > < span class = "line" > 23< / span > < br > < span class = "line" > 24< / span > < br > < span class = "line" > 25< / span > < br > < span class = "line" > 26< / span > < br > < span class = "line" > 27< / span > < br > < span class = "line" > 28< / span > < br > < span class = "line" > 29< / span > < br > < span class = "line" > 30< / span > < br > < span class = "line" > 31< / span > < br > < span class = "line" > 32< / span > < br > < span class = "line" > 33< / span > < br > < span class = "line" > 34< / span > < br > < span class = "line" > 35< / span > < br > < span class = "line" > 36< / span > < br > < span class = "line" > 37< / span > < br > < span class = "line" > 38< / span > < br > < span class = "line" > 39< / span > < br > < span class = "line" > 40< / span > < br > < span class = "line" > 41< / span > < br > < span class = "line" > 42< / span > < br > < span class = "line" > 43< / span > < br > < span class = "line" > 44< / span > < br > < span class = "line" > 45< / span > < br > < span class = "line" > 46< / span > < br > < span class = "line" > 47< / span > < br > < span class = "line" > 48< / span > < br > < span class = "line" > 49< / span > < br > < span class = "line" > 50< / span > < br > < span class = "line" > 51< / span > < br > < span class = "line" > 52< / span > < br > < / pre > < / td > < td class = "code" > < pre > < span class = "line" > < span class = "comment" > -- 数据准备< / span > < / span > < br > < span class = "line" > < span class = "comment" > -- 创建dept表， < / span > < / span > < br > < span class = "line" > < span class = "keyword" > create< / span > < span class = "keyword" > table< / span > dept< / span > < br > < span class = "line" > (< / span > < br > < span class = "line" > id < span class = "type" > int< / span > auto_increment comment < span class = "string" > ' ID' < / span > < span class = "keyword" > primary< / span > key,< / span > < br > < span class = "line" > name < span class = "type" > varchar< / span > (< span class = "number" > 50< / span > ) < span class = "keyword" > not< / span > < span class = "keyword" > null< / span > comment < span class = "string" > ' 部门名称' < / span > < / span > < br > < span class = "line" > ) comment < span class = "string" > ' 部门表' < / span > ;< / span > < br > < span class = "line" > < span class = "keyword" > INSERT< / span > < span class = "keyword" > INTO< / span > dept (id, name)< / span > < br > < span class = "line" > < span class = "keyword" > VALUES< / span > (< span class = "number" > 1< / span > , < span class = "string" > ' 研发部' < / span > ),< / span > < br > < span class = "line" > (< span class = "number" > 2< / span > , < span class = "string" > ' 市场部' < / span > ),< / span > < br > < span class = "line" > (< span class = "number" > 3< / span > , < span class = "string" > ' 财务部' < / span > ),< / span > < br > < span class = "line" > (< span class = "number" > 4< / span > ,< / span > < br > < span class = "line" > < span class = "string" > ' 销售部' < / span > ),< / span > < br > < span class = "line" > (< span class = "number" > 5< / span > , < span class = "string" > ' 总经办' < / span > ),< / span > < br > < span class = "line" > (< span class = "number" > 6< / span > , < span class = "string" > ' 人事部' < / span > );< / span > < br > < span class = "line" > < / span > < br > < span class = "line" > < span class = "comment" > -- 创建emp表， < / span > < / span > < br > < span class = "line" > < span class = "keyword" > create< / span > < span class = "keyword" > table< / span > emp< / span > < br > < span class = "line" > (< / span > < br > < span class = "line" > id < span class = "type" > int< / span > auto_increment comment < span class = "string
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< h4 id = "4-2-2-概述" > < a href = "#4-2-2-概述" class = "headerlink" title = "4.2.2 概述" > < / a > 4.2.2 概述< / h4 > < p > < img src = "/pictures/image-20231004200243641.png" alt = "image-20231004200243641" > < / p >
< h4 id = "4-2-3-分类" > < a href = "#4-2-3-分类" class = "headerlink" title = "4.2.3 分类" > < / a > 4.2.3 分类< / h4 > < p > < img src = "/pictures/image-20231004200624090.png" alt = "image-20231004200624090" > < / p >
< h3 id = "4-3-内连接" > < a href = "#4-3-内连接" class = "headerlink" title = "4.3 内连接" > < / a > 4.3 内连接< / h3 > < p > < img src = "/pictures/image-20231004200731770.png" alt = "image-20231004200731770" > < / p >
< figure class = "highlight sql" > < table > < tr > < td class = "gutter" > < pre > < span class = "line" > 1< / span > < br > < span class = "line" > 2< / span > < br > < span class = "line" > 3< / span > < br > < span class = "line" > 4< / span > < br > < span class = "line" > 5< / span > < br > < span class = "line" > 6< / span > < br > < span class = "line" > 7< / span > < br > < span class = "line" > 8< / span > < br > < span class = "line" > 9< / span > < br > < span class = "line" > 10< / span > < br > < span class = "line" > 11< / span > < br > < / pre > < / td > < td class = "code" > < pre > < span class = "line" > < span class = "comment" > -- 内连接演示< / span > < / span > < br > < span class = "line" > < span class = "comment" > -- 案例< / span > < / span > < br > < span class = "line" > < span class = "comment" > -- 查询每一个员工的姓名 , 及关联的部门的名称 (隐式内连接实现)< / span > < / span > < br > < span class = "line" > < span class = "comment" > -- 表结构: emp , dept< / span > < / span > < br > < span class = "line" > < span class = "comment" > -- 连接条件: emp.dept_id = dept.id< / span > < / span > < br > < span class = "line" > < span class = "keyword" > select< / span > e.name, d.name < span class = "keyword" > from< / span > emp e, dept d < span class = "keyword" > where< / span > e.dept_id < span class = "operator" > =< / span > d.id;< / span > < br > < span class = "line" > < / span > < br > < span class = "line" > < span class = "comment" > -- 查询每一个员工的姓名 , 及关联的部门的名称 (显式内连接实现) --- INNER JOIN ...ON ...< / span > < / span > < br > < span class = "line" > < span class = "comment" > -- 表结构: emp , dept< / span > < / span > < br > < span class = "line" > < span class = "comment" > -- 连接条件: emp.dept_id = dept.id< / span > < / span > < br > < span class = "line" > < span class = "keyword" > select< / span > e.name ,d.name < span class = "keyword" > from< / span > emp e < span class = "keyword" > inner< / span > < span class = "keyword" > join< / span > dept d < span class = "keyword" > on< / span > e.dept_id < span class = "operator" > =< / span > d.id;< / span > < br > < / pre > < / td > < / tr > < / table > < / figure >
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< blockquote >
< p > 一旦为表起了别名，就不能再使用表名来指定对应的字段了，此时只能够使用别名来指定字段。< / p >
< / blockquote >
< h3 id = "4-4-外连接" > < a href = "#4-4-外连接" class = "headerlink" title = "4.4 外连接" > < / a > 4.4 外连接< / h3 > < p > < img src = "/pictures/image-20231004201445881.png" alt = "image-20231004201445881" > < / p >
< figure class = "highlight sql" > < table > < tr > < td class = "gutter" > < pre > < span class = "line" > 1< / span > < br > < span class = "line" > 2< / span > < br > < span class = "line" > 3< / span > < br > < span class = "line" > 4< / span > < br > < span class = "line" > 5< / span > < br > < span class = "line" > 6< / span > < br > < span class = "line" > 7< / span > < br > < span class = "line" > 8< / span > < br > < span class = "line" > 9< / span > < br > < span class = "line" > 10< / span > < br > < span class = "line" > 11< / span > < br > < span class = "line" > 12< / span > < br > < / pre > < / td > < td class = "code" > < pre > < span class = "line" > < span class = "comment" > -- 外连接< / span > < / span > < br > < span class = "line" > < span class = "comment" > -- 查询emp表的所有数据, 和对应的部门信息< / span > < / span > < br > < span class = "line" > < span class = "comment" > -- 由于需求中提到， ， ， < / span > < / span > < br > < span class = "line" > < span class = "comment" > -- 表结构: emp, dept< / span > < / span > < br > < span class = "line" > < span class = "comment" > -- 连接条件: emp.dept_id = dept.id< / span > < / span > < br > < span class = "line" > < span class = "keyword" > select< / span > e.name,d.name < span class = "keyword" > from< / span > emp e < span class = "keyword" > left< / span > < span class = "keyword" > join< / span > dept d < span class = "keyword" > on< / span > e.dept_id < span class = "operator" > =< / span > d.id;< / span > < br > < span class = "line" > < / span > < br > < span class = "line" > < span class = "comment" > -- 查询dept表的所有数据, 和对应的员工信息(右外连接)< / span > < / span > < br > < span class = "line" > < span class = "comment" > -- 由于需求中提到， ， ， < / span > < / span > < br > < span class = "line" > < span class = "comment" > -- 表结构: emp, dept< / span > < / span > < br > < span class = "line" > < span class = "comment" > -- 连接条件: emp.dept_id = dept.id< / span > < / span > < br > < span class = "line" > < span class = "keyword" > select< / span > e.name,d.name < span class = "keyword" > from< / span > emp e < span class = "keyword" > right< / span > < span class = "keyword" > join< / span > dept d < span class = "keyword" > on< / span > e.dept_id < span class = "operator" > =< / span > d.id;< / span > < br > < / pre > < / td > < / tr > < / table > < / figure >
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< blockquote >
< p > 注意事项： ， ， ， < / p >
< / blockquote >
< h3 id = "4-5-自连接" > < a href = "#4-5-自连接" class = "headerlink" title = "4.5 自连接" > < / a > 4.5 自连接< / h3 > < p > < img src = "/pictures/image-20231004202219787.png" alt = "image-20231004202219787" > < / p >
< figure class = "highlight sql" > < table > < tr > < td class = "gutter" > < pre > < span class = "line" > 1< / span > < br > < span class = "line" > 2< / span > < br > < span class = "line" > 3< / span > < br > < span class = "line" > 4< / span > < br > < span class = "line" > 5< / span > < br > < span class = "line" > 6< / span > < br > < span class = "line" > 7< / span > < br > < span class = "line" > 8< / span > < br > < span class = "line" > 9< / span > < br > < / pre > < / td > < td class = "code" > < pre > < span class = "line" > < span class = "comment" > -- 自连接< / span > < / span > < br > < span class = "line" > < span class = "comment" > -- 查询员工 及其 所属领导的名字< / span > < / span > < br > < span class = "line" > < span class = "comment" > -- 表结构: emp< / span > < / span > < br > < span class = "line" > < span class = "comment" > -- 技巧:查询的时候看作是两张表< / span > < / span > < br > < span class = "line" > < span class = "keyword" > select< / span > e1.name < span class = "string" > ' 员工' < / span > ,e2.name < span class = "string" > ' 领导' < / span > < span class = "keyword" > from< / span > emp e1,emp e2 < span class = "keyword" > where< / span > e1.managerid < span class = "operator" > =< / span > e2.id;< / span > < br > < span class = "line" > < / span > < br > < span class = "line" > < span class = "comment" > -- 查询所有员工 emp 及其领导的名字 emp , 如果员工没有领导, 也需要查询出来< / span > < / span > < br > < span class = "line" > < span class = "comment" > -- 表结构: emp a , emp b< / span > < / span > < br > < span class = "line" > < span class = "keyword" > select< / span > e1.name < span class = "string" > ' 员工' < / span > ,e2.name < span class = "string" > ' 领导' < / span > < span class = "keyword" > from< / span > emp e1 < span class = "keyword" > left< / span > < span class = "keyword" > join< / span > emp e2 < span class = "keyword" > on< / span > e1.managerid < span class = "operator" > =< / span > e2.id;< / span > < br > < / pre > < / td > < / tr > < / table > < / figure >
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< h3 id = "4-6-联合查询" > < a href = "#4-6-联合查询" class = "headerlink" title = "4.6 联合查询" > < / a > 4.6 联合查询< / h3 > < p > < img src = "/pictures/image-20231004203207924.png" alt = "image-20231004203207924" > < / p >
< figure class = "highlight sql" > < table > < tr > < td class = "gutter" > < pre > < span class = "line" > 1< / span > < br > < span class = "line" > 2< / span > < br > < span class = "line" > 3< / span > < br > < span class = "line" > 4< / span > < br > < span class = "line" > 5< / span > < br > < span class = "line" > 6< / span > < br > < span class = "line" > 7< / span > < br > < / pre > < / td > < td class = "code" > < pre > < span class = "line" > < span class = "comment" > -- 联合查询< / span > < / span > < br > < span class = "line" > < span class = "comment" > -- 将薪资低于 5000 的员工 , 和 年龄大于 50 岁的员工全部查询出来.< / span > < / span > < br > < span class = "line" > < span class = "comment" > -- 当前对于这个需求，我们可以直接使用多条件查询，使用逻辑运算符 or 连接即可,也可以通过union/union all来联合查询< / span > < / span > < br > < span class = "line" > < span class = "comment" > -- 相当于把下面的两条sql的结果拼接在一起(去掉all就可以实现去重)< / span > < / span > < br > < span class = "line" > < span class = "keyword" > select< / span > < span class = "operator" > *< / span > < span class = "keyword" > from< / span > emp e < span class = "keyword" > where< / span > e.salary < span class = "operator" > < < / span > < span class = "number" > 5000< / span > < / span > < br > < span class = "line" > < span class = "keyword" > union< / span > < / span > < br > < span class = "line" > < span class = "keyword" > select< / span > < span class = "operator" > *< / span > < span class = "keyword" > from< / span > emp e < span class = "keyword" > where< / span > e.age < span class = "operator" > > < / span > < span class = "number" > 50< / span > ;< / span > < br > < / pre > < / td > < / tr > < / table > < / figure >
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< p > < img src = "/pictures/image-20231004203724124.png" alt = "image-20231004203724124" > < / p >
< blockquote >
< p > union all查询出来的结果， ， < / p >
< p > union 联合查询，会对查询出来的结果进行去重处理< / p >
< / blockquote >
< h3 id = "4-7-子查询" > < a href = "#4-7-子查询" class = "headerlink" title = "4.7 子查询" > < / a > 4.7 子查询< / h3 > < p > < img src = "/pictures/image-20231004204033345.png" alt = "image-20231004204033345" > < / p >
< p > < strong > 标量子查询< / strong > < / p >
< p > 子查询返回的结果是单个值（数字、字符串、日期等），最简单的形式，这种子查询称为标量子查询。常用的操作符：= < > > > = < < = < / p >
< figure class = "highlight sql" > < table > < tr > < td class = "gutter" > < pre > < span class = "line" > 1< / span > < br > < span class = "line" > 2< / span > < br > < span class = "line" > 3< / span > < br > < span class = "line" > 4< / span > < br > < span class = "line" > 5< / span > < br > < span class = "line" > 6< / span > < br > < span class = "line" > 7< / span > < br > < / pre > < / td > < td class = "code" > < pre > < span class = "line" > < span class = "comment" > -- 标量子查询< / span > < / span > < br > < span class = "line" > < span class = "comment" > -- 1.查询 " 销售部" 的所有员工信息< / span > < / span > < br > < span class = "line" > < span class = "comment" > -- 1.1 查询销售部的部门id< / span > < / span > < br > < span class = "line" > < span class = "keyword" > select< / span > < span class = "operator" > *< / span > < span class = "keyword" > from< / span > emp e < span class = "keyword" > where< / span > e.dept_id < span class = "operator" > =< / span > (< span class = "keyword" > select< / span > id < span class = "keyword" > from< / span > dept d < span class = "keyword" > where< / span > d.name < span class = "operator" > =< / span > < span class = "string" > ' 销售部' < / span > );< / span > < br > < span class = "line" > < / span > < br > < span class = "line" > < span class = "comment" > -- 查询在 " 方东白" 入职之后的员工信息< / span > < / span > < br > < span class = "line" > < span class = "keyword" > select< / span > < span class = "operator" > *< / span > < span class = "keyword" > from< / span > emp e1 < span class = "keyword" > where< / span > e1.entrydate < span class = "operator" > > < / span > (< span class = "keyword" > select< / span > e2.entrydate < span class = "keyword" > from< / span > emp e2 < span class = "keyword" > where< / span > e2.name < span class = "operator" > =< / span > < span class = "string" > ' 方东白' < / span > );< / span > < br > < / pre > < / td > < / tr > < / table > < / figure >
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< p > < strong > 列子查询< / strong > < / p >
< p > 子查询返回的结果是一列（ ） ， ： < / p >
< p > < img src = "/pictures/image-20231004205225188.png" alt = "image-20231004205225188" > < / p >
< figure class = "highlight sql" > < table > < tr > < td class = "gutter" > < pre > < span class = "line" > 1< / span > < br > < span class = "line" > 2< / span > < br > < span class = "line" > 3< / span > < br > < span class = "line" > 4< / span > < br > < span class = "line" > 5< / span > < br > < span class = "line" > 6< / span > < br > < span class = "line" > 7< / span > < br > < span class = "line" > 8< / span > < br > < span class = "line" > 9< / span > < br > < / pre > < / td > < td class = "code" > < pre > < span class = "line" > < span class = "comment" > -- 列子查询< / span > < / span > < br > < span class = "line" > < span class = "comment" > -- 查询 " 销售部" 和 " 市场部" 的所有员工信息< / span > < / span > < br > < span class = "line" > < span class = "keyword" > select< / span > < span class = "operator" > *< / span > < span class = "keyword" > from< / span > emp e < span class = "keyword" > where< / span > e.dept_id < span class = "keyword" > in< / span > (< span class = "keyword" > select< / span > id < span class = "keyword" > from< / span > dept < span class = "keyword" > where< / span > dept.name < span class = "operator" > =< / span > < span class = "string" > ' 销售部' < / span > < span class = "keyword" > or< / span > dept.name < span class = "operator" > =< / span > < span class = "string" > ' 市场部' < / span > );< / span > < br > < span class = "line" > < / span > < br > < span class = "line" > < span class = "comment" > -- 查询比财务部所有人工资都高的员工信息< / span > < / span > < br > < span class = "line" > < span class = "keyword" > select< / span > < span class = "operator" > *< / span > < span class = "keyword" > from< / span > emp e < span class = "keyword" > where< / span > e.salary < span class = "operator" > > < / span > < span class = "keyword" > all< / span > (< span class = "keyword" > select< / span > e2.salary < span class = "keyword" > from< / span > emp e2 < span class = "keyword" > where< / span > e2.dept_id < span class = "operator" > =< / span > (< span class = "keyword" > select< / span > id < span class = "keyword" > from< / span > dept < span class = "keyword" > where< / span > dept.name < span class = "operator" > =< / span > < span class = "string" > ' 财务部' < / span > ));< / span > < br > < span class = "line" > < / span > < br > < span class = "line" > < span class = "comment" > -- 查询比研发部其中任意一人工资高的员工信息(使用any或者some均可)< / span > < / span > < br > < span class = "line" > < span class = "keyword" > select< / span > < span class = "operator" > *< / span > < span class = "keyword" > from< / span > emp e < span class = "keyword" > where< / span > e.salary < span class = "operator" > > < / span > < span class = "keyword" > any< / span > (< span class = "keyword" > select< / span > e2.salary < span class = "keyword" > from< / span > emp e2 < span class = "keyword" > where< / span > e2.dept_id < span class = "operator" > =< / span > (< span class = "keyword" > select< / span > id < span class = "keyword" > from< / span > dept < span class = "keyword" > where< / span > dept.name < span class = "operator" > =< / span > < span class = "string" > ' 研发部' < / span > ));< / span > < br > < / pre > < / td > < / tr > < / table > < / figure >
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< p > < strong > 行子查询< / strong > < / p >
< p > 子查询返回的结果是一行（可以是多列），这种子查询称为行子查询。常用的操作符：= 、< > 、IN 、NOT IN< / p >
< figure class = "highlight sql" > < table > < tr > < td class = "gutter" > < pre > < span class = "line" > 1< / span > < br > < span class = "line" > 2< / span > < br > < span class = "line" > 3< / span > < br > < / pre > < / td > < td class = "code" > < pre > < span class = "line" > < span class = "comment" > -- 行子查询< / span > < / span > < br > < span class = "line" > < span class = "comment" > -- 查询与" 张无忌" 的薪资及与其直属领导相同的员工信息< / span > < / span > < br > < span class = "line" > < span class = "keyword" > select< / span > < span class = "operator" > *< / span > < span class = "keyword" > from< / span > emp e2 < span class = "keyword" > where< / span > (e2.salary,e2.managerid) < span class = "operator" > =< / span > (< span class = "keyword" > select< / span > e.salary,e.managerid < span class = "keyword" > from< / span > emp e < span class = "keyword" > where< / span > e.name < span class = "operator" > =< / span > < span class = "string" > ' 张无忌' < / span > );< / span > < br > < / pre > < / td > < / tr > < / table > < / figure >
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< p > < strong > 表子查询< / strong > < / p >
< p > 子查询返回的结果是多行多列， ： < / p >
< figure class = "highlight sql" > < table > < tr > < td class = "gutter" > < pre > < span class = "line" > 1< / span > < br > < span class = "line" > 2< / span > < br > < span class = "line" > 3< / span > < br > < span class = "line" > 4< / span > < br > < span class = "line" > 5< / span > < br > < span class = "line" > 6< / span > < br > < / pre > < / td > < td class = "code" > < pre > < span class = "line" > < span class = "comment" > -- 表子查询< / span > < / span > < br > < span class = "line" > < span class = "comment" > -- 查询与 " 鹿杖客" , " 宋远桥" 的职位和薪资相同的员工信息< / span > < / span > < br > < span class = "line" > < span class = "keyword" > select< / span > < span class = "operator" > *< / span > < span class = "keyword" > from< / span > emp e2 < span class = "keyword" > where< / span > (e2.job,e2.salary) < span class = "keyword" > in< / span > (< span class = "keyword" > select< / span > e.job, e.salary < span class = "keyword" > from< / span > emp e < span class = "keyword" > where< / span > e.name < span class = "operator" > =< / span > < span class = "string" > ' 鹿杖客' < / span > < span class = "keyword" > or< / span > name < span class = "operator" > =< / span > < span class = "string" > ' 宋远桥' < / span > );< / span > < br > < span class = "line" > < / span > < br > < span class = "line" > < span class = "comment" > -- 查询入职日期是 " 2006-01-01" 之后的员工信息 , 及其部门信息< / span > < / span > < br > < span class = "line" > < span class = "keyword" > select< / span > < span class = "operator" > *< / span > < span class = "keyword" > from< / span > (< span class = "keyword" > select< / span > < span class = "operator" > *< / span > < span class = "keyword" > from< / span > emp < span class = "keyword" > where< / span > entrydate < span class = "operator" > > < / span > < span class = "string" > ' 2006-01-01' < / span > ) e < span class = "keyword" > left< / span > < span class = "keyword" > join< / span > dept d < span class = "keyword" > on< / span > e.dept_id < span class = "operator" > =< / span > d.id;< / span > < br > < / pre > < / td > < / tr > < / table > < / figure >
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< p > < strong > 多表查询相关的sql语句< / strong > < / p >
< figure class = "highlight sql" > < table > < tr > < td class = "gutter" > < pre > < span class = "line" > 1< / span > < br > < span class = "line" > 2< / span > < br > < span class = "line" > 3< / span > < br > < span class = "line" > 4< / span > < br > < span class = "line" > 5< / span > < br > < span class = "line" > 6< / span > < br > < span class = "line" > 7< / span > < br > < span class = "line" > 8< / span > < br > < span class = "line" > 9< / span > < br > < span class = "line" > 10< / span > < br > < span class = "line" > 11< / span > < br > < span class = "line" > 12< / span > < br > < span class = "line" > 13< / span > < br > < span class = "line" > 14< / span > < br > < span class = "line" > 15< / span > < br > < span class = "line" > 16< / span > < br > < span class = "line" > 17< / span > < br > < span class = "line" > 18< / span > < br > < span class = "line" > 19< / span > < br > < span class = "line" > 20< / span > < br > < span class = "line" > 21< / span > < br > < span class = "line" > 22< / span > < br > < span class = "line" > 23< / span > < br > < span class = "line" > 24< / span > < br > < span class = "line" > 25< / span > < br > < span class = "line" > 26< / span > < br > < span class = "line" > 27< / span > < br > < span class = "line" > 28< / span > < br > < span class = "line" > 29< / span > < br > < span class = "line" > 30< / span > < br > < span class = "line" > 31< / span > < br > < span class = "line" > 32< / span > < br > < span class = "line" > 33< / span > < br > < span class = "line" > 34< / span > < br > < span class = "line" > 35< / span > < br > < span class = "line" > 36< / span > < br > < span class = "line" > 37< / span > < br > < span class = "line" > 38< / span > < br > < span class = "line" > 39< / span > < br > < span class = "line" > 40< / span > < br > < span class = "line" > 41< / span > < br > < span class = "line" > 42< / span > < br > < span class = "line" > 43< / span > < br > < span class = "line" > 44< / span > < br > < span class = "line" > 45< / span > < br > < span class = "line" > 46< / span > < br > < span class = "line" > 47< / span > < br > < span class = "line" > 48< / span > < br > < span class = "line" > 49< / span > < br > < span class = "line" > 50< / span > < br > < span class = "line" > 51< / span > < br > < span class = "line" > 52< / span > < br > < span class = "line" > 53< / span > < br > < span class = "line" > 54< / span > < br > < span class = "line" > 55< / span > < br > < span class = "line" > 56< / span > < br > < span class = "line" > 57< / span > < br > < span class = "line" > 58< / span > < br > < span class = "line" > 59< / span > < br > < span class = "line" > 60< / span > < br > < span class = "line" > 61< / span > < br > < span class = "line" > 62< / span > < br > < span class = "line" > 63< / span > < br > < span class = "line" > 64< / span > < br > < span class = "line" > 65< / span > < br > < span class = "line" > 66< / span > < br > < span class = "line" > 67< / span > < br > < span class = "line" > 68< / span > < br > < span class = "line" > 69< / span > < br > < span class = "line" > 70< / span > < br > < span class = "line" > 71< / span > < br > < span class = "line" > 72< / span > < br > < span class = "line" > 73< / span > < br > < span class = "line" > 74< / span > < br > < span class = "line" > 75< / span > < br > < span class = "line" > 76< / span > < br > < span class = "line" > 77< / span > < br > < span class = "line" > 78< / span > < br > < span class = "line" > 79< / span > < br > < span class = "line" > 80< / span > < br > < span class = "line" > 81< / span > < br > < span class = "line" > 82< / span > < br > < span class = "line" > 83< / span > < br > < span class = "line" > 84< / span > < br > < span class = "line" > 85< / span > < br > < span class = "line" > 86< / span > < br > < span class = "line" > 87< / span > < br > < span class = "line" > 88< / span > < br > < span class = "line" > 89< / span > < br > < span class = "line" > 90< / span > < br > < span class = "line" > 91< / span > < br > < span class = "line" > 92< / span > < br > < span class = "line" > 93< / span > < br > < span class = "line" > 94< / span > < br > < span class = "line" > 95< / span > < br > < span class = "line" > 96< / span > < br > < span class = "line" > 97< / span > < br > < span class = "line" > 98< / span > < br > < span class = "line" > 99< / span > < br > < span class = "line" > 100< / span > < br > < span class = "line" > 101< / span > < br > < span class = "line" > 102< / span > < br > < span class = "line" > 103< / span > < br > < span class = "line" > 104< / span > < br > < span class = "line" > 105< / span > < br > < span class = "line" > 106< / span > < br > < span class = "line" > 107< / span > < br > < span class = "line" > 108< / span > < br > < span class = "line" > 109< / span > < br > < span class = "line" > 110< / span > < br > < span class = "line" > 111< / span > < br > < span class = "line" > 112< / span > < br > < span class = "line" > 113< / span > < br > < span class = "line" > 114< / span > < br > < span class = "line" > 115< / span > < br > < span class = "line" > 116< / span > < br > < span class = "line" > 117< / span > < br > < span class = "line" > 118< / span > < br > < span class = "line" > 119< / span > < br > < span class = "line" > 120< / span > < br > < span class = "line" > 121< / span > < br > < span class = "line" > 122< / span > < br > < span class = "line" > 123< / span > < br > < span class = "line" > 124< / span > < br > < span class = "line" > 125< / span > < br > < span class = "
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< h3 id = "4-8-多表查询案例" > < a href = "#4-8-多表查询案例" class = "headerlink" title = "4.8 多表查询案例" > < / a > 4.8 多表查询案例< / h3 > < p > < strong > 题目< / strong > < / p >
< p > < img src = "/pictures/image-20231004212719134.png" alt = "image-20231004212719134" > < / p >
< p > < strong > 数据准备< / strong > < / p >
< figure class = "highlight sql" > < table > < tr > < td class = "gutter" > < pre > < span class = "line" > 1< / span > < br > < span class = "line" > 2< / span > < br > < span class = "line" > 3< / span > < br > < span class = "line" > 4< / span > < br > < span class = "line" > 5< / span > < br > < span class = "line" > 6< / span > < br > < span class = "line" > 7< / span > < br > < span class = "line" > 8< / span > < br > < span class = "line" > 9< / span > < br > < span class = "line" > 10< / span > < br > < span class = "line" > 11< / span > < br > < span class = "line" > 12< / span > < br > < span class = "line" > 13< / span > < br > < span class = "line" > 14< / span > < br > < span class = "line" > 15< / span > < br > < span class = "line" > 16< / span > < br > < span class = "line" > 17< / span > < br > < span class = "line" > 18< / span > < br > < span class = "line" > 19< / span > < br > < span class = "line" > 20< / span > < br > < span class = "line" > 21< / span > < br > < span class = "line" > 22< / span > < br > < span class = "line" > 23< / span > < br > < span class = "line" > 24< / span > < br > < span class = "line" > 25< / span > < br > < span class = "line" > 26< / span > < br > < span class = "line" > 27< / span > < br > < span class = "line" > 28< / span > < br > < span class = "line" > 29< / span > < br > < span class = "line" > 30< / span > < br > < span class = "line" > 31< / span > < br > < span class = "line" > 32< / span > < br > < span class = "line" > 33< / span > < br > < span class = "line" > 34< / span > < br > < span class = "line" > 35< / span > < br > < span class = "line" > 36< / span > < br > < span class = "line" > 37< / span > < br > < span class = "line" > 38< / span > < br > < span class = "line" > 39< / span > < br > < span class = "line" > 40< / span > < br > < span class = "line" > 41< / span > < br > < span class = "line" > 42< / span > < br > < span class = "line" > 43< / span > < br > < span class = "line" > 44< / span > < br > < span class = "line" > 45< / span > < br > < span class = "line" > 46< / span > < br > < span class = "line" > 47< / span > < br > < span class = "line" > 48< / span > < br > < span class = "line" > 49< / span > < br > < span class = "line" > 50< / span > < br > < span class = "line" > 51< / span > < br > < span class = "line" > 52< / span > < br > < span class = "line" > 53< / span > < br > < span class = "line" > 54< / span > < br > < span class = "line" > 55< / span > < br > < span class = "line" > 56< / span > < br > < span class = "line" > 57< / span > < br > < span class = "line" > 58< / span > < br > < span class = "line" > 59< / span > < br > < span class = "line" > 60< / span > < br > < span class = "line" > 61< / span > < br > < span class = "line" > 62< / span > < br > < span class = "line" > 63< / span > < br > < span class = "line" > 64< / span > < br > < span class = "line" > 65< / span > < br > < span class = "line" > 66< / span > < br > < span class = "line" > 67< / span > < br > < span class = "line" > 68< / span > < br > < span class = "line" > 69< / span > < br > < span class = "line" > 70< / span > < br > < span class = "line" > 71< / span > < br > < span class = "line" > 72< / span > < br > < span class = "line" > 73< / span > < br > < span class = "line" > 74< / span > < br > < span class = "line" > 75< / span > < br > < span class = "line" > 76< / span > < br > < / pre > < / td > < td class = "code" > < pre > < span class = "line" > < span class = "comment" > -- 数据准备< / span > < / span > < br > < span class = "line" > < span class = "comment" > -- 创建dept表， < / span > < / span > < br > < span class = "line" > < span class = "keyword" > create< / span > < span class = "keyword" > table< / span > dept< / span > < br > < span class = "line" > (< / span > < br > < span class = "line" > id < span class = "type" > int< / span > auto_increment comment < span class = "string" > ' ID' < / span > < span class = "keyword" > primary< / span > key,< / span > < br > < span class = "line" > name < span class = "type" > varchar< / span > (< span class = "number" > 50< / span > ) < span class = "keyword" > not< / span > < span class = "keyword" > null< / span > comment < span class = "string" > ' 部门名称' < / span > < / span > < br > < span class = "line" > ) comment < span class = "string" > ' 部门表' < / span > ;< / span > < br > < span class = "line" > < span class = "keyword" > INSERT< / span > < span class = "keyword" > INTO< / span > dept (id, name)< / span > < br > < span class = "line" > < span class = "keyword" > VALUES< / span > (< span class = "number" > 1< / span > , < span class = "string" > ' 研发部' < / span > ),< / span > < br > < span class = "line" > (< span class = "number" > 2< / span > , < span class = "string" > ' 市场部' < / span > ),< / span > < br > < span class = "line" > (< span class = "number" > 3< / span > , < span class = "string" > ' 财务部' < / span > ),< / span > < br > < span class = "line" > (< span class = "number" > 4< / span > ,< / span > < br > < span class = "line" > < span class = "string" > ' 销售部' < / span > ),< / span > < br > < span class = "line" > (< span class = "number" > 5< / span > , < span class = "string" > ' 总经办' < / span > ),< /s
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< p > < strong > 题解< / strong > < / p >
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< figure class = "highlight sql" > < table > < tr > < td class = "gutter" > < pre > < span class = "line" > 1< / span > < br > < span class = "line" > 2< / span > < br > < span class = "line" > 3< / span > < br > < span class = "line" > 4< / span > < br > < span class = "line" > 5< / span > < br > < span class = "line" > 6< / span > < br > < span class = "line" > 7< / span > < br > < span class = "line" > 8< / span > < br > < span class = "line" > 9< / span > < br > < span class = "line" > 10< / span > < br > < span class = "line" > 11< / span > < br > < span class = "line" > 12< / span > < br > < span class = "line" > 13< / span > < br > < span class = "line" > 14< / span > < br > < span class = "line" > 15< / span > < br > < span class = "line" > 16< / span > < br > < span class = "line" > 17< / span > < br > < span class = "line" > 18< / span > < br > < span class = "line" > 19< / span > < br > < span class = "line" > 20< / span > < br > < span class = "line" > 21< / span > < br > < span class = "line" > 22< / span > < br > < span class = "line" > 23< / span > < br > < span class = "line" > 24< / span > < br > < span class = "line" > 25< / span > < br > < span class = "line" > 26< / span > < br > < span class = "line" > 27< / span > < br > < span class = "line" > 28< / span > < br > < span class = "line" > 29< / span > < br > < span class = "line" > 30< / span > < br > < span class = "line" > 31< / span > < br > < span class = "line" > 32< / span > < br > < span class = "line" > 33< / span > < br > < span class = "line" > 34< / span > < br > < span class = "line" > 35< / span > < br > < span class = "line" > 36< / span > < br > < span class = "line" > 37< / span > < br > < span class = "line" > 38< / span > < br > < span class = "line" > 39< / span > < br > < span class = "line" > 40< / span > < br > < span class = "line" > 41< / span > < br > < span class = "line" > 42< / span > < br > < span class = "line" > 43< / span > < br > < span class = "line" > 44< / span > < br > < span class = "line" > 45< / span > < br > < span class = "line" > 46< / span > < br > < span class = "line" > 47< / span > < br > < span class = "line" > 48< / span > < br > < span class = "line" > 49< / span > < br > < span class = "line" > 50< / span > < br > < span class = "line" > 51< / span > < br > < span class = "line" > 52< / span > < br > < span class = "line" > 53< / span > < br > < span class = "line" > 54< / span > < br > < span class = "line" > 55< / span > < br > < span class = "line" > 56< / span > < br > < span class = "line" > 57< / span > < br > < span class = "line" > 58< / span > < br > < span class = "line" > 59< / span > < br > < span class = "line" > 60< / span > < br > < span class = "line" > 61< / span > < br > < span class = "line" > 62< / span > < br > < span class = "line" > 63< / span > < br > < span class = "line" > 64< / span > < br > < span class = "line" > 65< / span > < br > < span class = "line" > 66< / span > < br > < span class = "line" > 67< / span > < br > < span class = "line" > 68< / span > < br > < span class = "line" > 69< / span > < br > < span class = "line" > 70< / span > < br > < span class = "line" > 71< / span > < br > < span class = "line" > 72< / span > < br > < span class = "line" > 73< / span > < br > < span class = "line" > 74< / span > < br > < span class = "line" > 75< / span > < br > < span class = "line" > 76< / span > < br > < span class = "line" > 77< / span > < br > < span class = "line" > 78< / span > < br > < span class = "line" > 79< / span > < br > < span class = "line" > 80< / span > < br > < span class = "line" > 81< / span > < br > < span class = "line" > 82< / span > < br > < span class = "line" > 83< / span > < br > < span class = "line" > 84< / span > < br > < span class = "line" > 85< / span > < br > < span class = "line" > 86< / span > < br > < span class = "line" > 87< / span > < br > < span class = "line" > 88< / span > < br > < span class = "line" > 89< / span > < br > < span class = "line" > 90< / span > < br > < span class = "line" > 91< / span > < br > < span class = "line" > 92< / span > < br > < span class = "line" > 93< / span > < br > < span class = "line" > 94< / span > < br > < span class = "line" > 95< / span > < br > < span class = "line" > 96< / span > < br > < span class = "line" > 97< / span > < br > < span class = "line" > 98< / span > < br > < span class = "line" > 99< / span > < br > < span class = "line" > 100< / span > < br > < span class = "line" > 101< / span > < br > < / pre > < / td > < td class = "code" > < pre > < span class = "line" > < span class = "comment" > -- 题解< / span > < / span > < br > < span class = "line" > < span class = "comment" > -- 1.查询员工的姓名、年龄、职位、部门信息（隐式内连接）< / span > < / span > < br > < span class = "line" > < span class = "keyword" > select< / span > e.name, e.age, e.job, d.name< / span > < br > < span class = "line" > < span class = "keyword" > from< / span > emp e,< / span > < br > < span class = "line" > dept d< / span > < br > < span class = "line" > < span class = "keyword" > where< / span > e.dept_id < span class = "operator" > =< / span > d.id;< / span > < br > < span class = "line" > < / span > < br > < span class = "line" > < span class = "comment" > -- 2.查询年龄小于30岁的员工的姓名、年龄、职位、部门信息（ ） < / span > < / span > < br > < span class = "line" > < span class = "keyword" > select< / span > e.na
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< p > < strong > 总结< / strong > < / p >
< p > < img src = "/pictures/image-20231005133456395.png" alt = "image-20231005133456395" > < / p >
< h2 id = "5-事务" > < a href = "#5-事务" class = "headerlink" title = "5.事务" > < / a > 5.事务< / h2 > < h3 id = "5-1-事务介绍" > < a href = "#5-1-事务介绍" class = "headerlink" title = "5.1 事务介绍" > < / a > 5.1 事务介绍< / h3 > < p > ， ， < / p >
< blockquote >
< p > 注意： 默认MySQL的事务是自动提交的， ， ， < / p >
< / blockquote >
< h3 id = "5-2-事务操作" > < a href = "#5-2-事务操作" class = "headerlink" title = "5.2 事务操作" > < / a > 5.2 事务操作< / h3 > < p > < strong > 数据准备< / strong > < / p >
< figure class = "highlight sql" > < table > < tr > < td class = "gutter" > < pre > < span class = "line" > 1< / span > < br > < span class = "line" > 2< / span > < br > < span class = "line" > 3< / span > < br > < span class = "line" > 4< / span > < br > < span class = "line" > 5< / span > < br > < span class = "line" > 6< / span > < br > < span class = "line" > 7< / span > < br > < span class = "line" > 8< / span > < br > < span class = "line" > 9< / span > < br > < span class = "line" > 10< / span > < br > < span class = "line" > 11< / span > < br > < span class = "line" > 12< / span > < br > < span class = "line" > 13< / span > < br > < span class = "line" > 14< / span > < br > < span class = "line" > 15< / span > < br > < span class = "line" > 16< / span > < br > < span class = "line" > 17< / span > < br > < span class = "line" > 18< / span > < br > < span class = "line" > 19< / span > < br > < span class = "line" > 20< / span > < br > < span class = "line" > 21< / span > < br > < span class = "line" > 22< / span > < br > < / pre > < / td > < td class = "code" > < pre > < span class = "line" > < span class = "comment" > -- 数据准备< / span > < / span > < br > < span class = "line" > < span class = "keyword" > drop< / span > < span class = "keyword" > table< / span > if < span class = "keyword" > exists< / span > account;< / span > < br > < span class = "line" > < span class = "keyword" > create< / span > < span class = "keyword" > table< / span > account< / span > < br > < span class = "line" > (< / span > < br > < span class = "line" > id < span class = "type" > int< / span > < span class = "keyword" > primary< / span > key AUTO_INCREMENT comment < span class = "string" > ' ID' < / span > ,< / span > < br > < span class = "line" > name < span class = "type" > varchar< / span > (< span class = "number" > 10< / span > ) comment < span class = "string" > ' 姓名' < / span > ,< / span > < br > < span class = "line" > money < span class = "keyword" > double< / span > (< span class = "number" > 10< / span > , < span class = "number" > 2< / span > ) comment < span class = "string" > ' 余额' < / span > < / span > < br > < span class = "line" > ) comment < span class = "string" > ' 账户表' < / span > ;< / span > < br > < span class = "line" > < span class = "keyword" > insert< / span > < span class = "keyword" > into< / span > account(name, money)< / span > < br > < span class = "line" > < span class = "keyword" > VALUES< / span > (< span class = "string" > ' 张三' < / span > , < span class = "number" > 2000< / span > ),< / span > < br > < span class = "line" > (< span class = "string" > ' 李四' < / span > , < span class = "number" > 2000< / span > );< / span > < br > < span class = "line" > < span class = "keyword" > select< / span > < span class = "operator" > *< / span > < span class = "keyword" > from< / span > account;< / span > < br > < span class = "line" > < / span > < br > < span class = "line" > < / span > < br > < span class = "line" > < / span > < br > < span class = "line" > < span class = "comment" > -- 转账操作（ ） < / span > < / span > < br > < span class = "line" > < span class = "comment" > -- 1. 查询张三余额< / span > < / span > < br > < span class = "line" > < span class = "keyword" > select< / span > < span class = "operator" > *< / span > < span class = "keyword" > from< / span > account < span class = "keyword" > where< / span > name < span class = "operator" > =< / span > < span class = "string" > ' 张三' < / span > ;< / span > < br > < span class = "line" > < span class = "comment" > -- 2. 张三的余额减少1000< / span > < / span > < br > < span class = "line" > < span class = "keyword" > update< / span > account < span class = "keyword" > set< / span > money < span class = "operator" > =< / span > money < span class = "operator" > -< / span > < span class = "number" > 1000< / span > < span class = "keyword" > where< / span > name < span class = "operator" > =< / span > < span class = "string" > ' 张三' < / span > ;< / span > < br > < span class = "line" > < span class = "comment" > -- 3. 李四的余额增加1000< / span > < / span > < br > < span class = "line" > < span class = "keyword" > update< / span > account < span class = "keyword" > set< / span > money < span class = "operator" > =< / span > money < span class = "operator" > +< / span > < span class = "number" > 1000< / span > < span class = "keyword" > where< / span > name < span class = "operator" > =< / span > < span class = "string" > ' 李四' < / span > ;< / span > < br > < / pre > < / td > < / tr > < / table > < / figure >
< p > < strong > 控制事务一< / strong > < / p >
< p > < img src = "/pictures/image-20231005134601982.png" alt = "image-20231005134601982" > < / p >
< p > < strong > 控制事务二< / strong > < / p >
< p > < img src = "/pictures/image-20231005134750027.png" alt = "image-20231005134750027" > < / p >
< p > < img src = "/pictures/image-20231005134835921.png" alt = "image-20231005134835921" > < / p >
< figure class = "highlight sql" > < table > < tr > < td class = "gutter" > < pre > < span class = "line" > 1< / span > < br > < span class = "line" > 2< / span > < br > < span class = "line" > 3< / span > < br > < span class = "line" > 4< / span > < br > < span class = "line" > 5< / span > < br > < span class = "line" > 6< / span > < br > < span class = "line" > 7< / span > < br > < span class = "line" > 8< / span > < br > < span class = "line" > 9< / span > < br > < span class = "line" > 10< / span > < br > < span class = "line" > 11< / span > < br > < span class = "line" > 12< / span > < br > < / pre > < / td > < td class = "code" > < pre > < span class = "line" > < span class = "comment" > -- 开启事务< / span > < / span > < br > < span class = "line" > < span class = "keyword" > start< / span > transaction;< / span > < br > < span class = "line" > < span class = "comment" > -- 1. 查询张三余额< / span > < / span > < br > < span class = "line" > < span class = "keyword" > select< / span > < span class = "operator" > *< / span > < span class = "keyword" > from< / span > account < span class = "keyword" > where< / span > name < span class = "operator" > =< / span > < span class = "string" > ' 张三' < / span > ;< / span > < br > < span class = "line" > < span class = "comment" > -- 2. 张三的余额减少1000< / span > < / span > < br > < span class = "line" > < span class = "keyword" > update< / span > account < span class = "keyword" > set< / span > money < span class = "operator" > =< / span > money < span class = "operator" > -< / span > < span class = "number" > 1000< / span > < span class = "keyword" > where< / span > name < span class = "operator" > =< / span > < span class = "string" > ' 张三' < / span > ;< / span > < br > < span class = "line" > < span class = "comment" > -- 3. 李四的余额增加1000< / span > < / span > < br > < span class = "line" > < span class = "keyword" > update< / span > account < span class = "keyword" > set< / span > money < span class = "operator" > =< / span > money < span class = "operator" > +< / span > < span class = "number" > 1000< / span > < span class = "keyword" > where< / span > name < span class = "operator" > =< / span > < span class = "string" > ' 李四' < / span > ;< / span > < br > < span class = "line" > < span class = "comment" > -- 如果正常执行完毕, 则提交事务< / span > < / span > < br > < span class = "line" > < span class = "keyword" > commit< / span > ;< / span > < br > < span class = "line" > < span class = "comment" > -- 如果执行过程中报错, 则回滚事务< / span > < / span > < br > < span class = "line" > < span class = "comment" > -- rollback;< / span > < / span > < br > < / pre > < / td > < / tr > < / table > < / figure >
< h3 id = "5-3-事务四大特性" > < a href = "#5-3-事务四大特性" class = "headerlink" title = "5.3 事务四大特性" > < / a > 5.3 事务四大特性< / h3 > < p > < img src = "/pictures/image-20231005135637347.png" alt = "image-20231005135637347" > < / p >
< h3 id = "5-4-并发事务问题" > < a href = "#5-4-并发事务问题" class = "headerlink" title = "5.4 并发事务问题" > < / a > 5.4 并发事务问题< / h3 > < p > < img src = "/pictures/image-20231005135741486.png" alt = "image-20231005135741486" > < / p >
< p > < img src = "/pictures/image-20231005135811745.png" alt = "image-20231005135811745" > < / p >
< h3 id = "5-5-事务隔离级别" > < a href = "#5-5-事务隔离级别" class = "headerlink" title = "5.5 事务隔离级别" > < / a > 5.5 事务隔离级别< / h3 > < p > < strong > 为了解决并发事务所引发的问题，在数据库中引入了事务隔离级别，主要有以下几种：< / strong > < / p >
< p > < / p >
< p > < img src = "/pictures/image-20231005140255060.png" alt = "image-20231005140255060" > < / p >
< p > < img src = "/pictures/image-20231005140322039.png" alt = "image-20231005140322039" > < / p >
< figure class = "highlight sql" > < table > < tr > < td class = "gutter" > < pre > < span class = "line" > 1< / span > < br > < span class = "line" > 2< / span > < br > < span class = "line" > 3< / span > < br > < span class = "line" > 4< / span > < br > < span class = "line" > 5< / span > < br > < / pre > < / td > < td class = "code" > < pre > < span class = "line" > < span class = "comment" > -- 查看事务隔离级别< / span > < / span > < br > < span class = "line" > < span class = "keyword" > SELECT< / span > @< span class = "variable" > @TRANSACTION_ISOLATION< / span > ;< / span > < br > < span class = "line" > < / span > < br > < span class = "line" > < span class = "comment" > -- 设置事务的隔离级别< / span > < / span > < br > < span class = "line" > < span class = "keyword" > SET< / span > [ SESSION < span class = "operator" > |< / span > < span class = "keyword" > GLOBAL< / span > ] TRANSACTION ISOLATION LEVEL { READ UNCOMMITTED < span class = "operator" > |< / span > READ COMMITTED < span class = "operator" > |< / span > REPEATABLE READ < span class = "operator" > |< / span > SERIALIZABLE } < / span > < br > < / pre > < / td > < / tr > < / table > < / figure >
< p > < strong > 小结< / strong > < / p >
< p > < img src = "/pictures/image-20231005142056902.png" alt = "image-20231005142056902" > < / p >
< p > < strong > 基础篇全部的Sql< / strong > < / p >
< figure class = "highlight sql" > < table > < tr > < td class = "gutter" > < pre > < span class = "line" > 1< / span > < br > < span class = "line" > 2< / span > < br > < span class = "line" > 3< / span > < br > < span class = "line" > 4< / span > < br > < span class = "line" > 5< / span > < br > < span class = "line" > 6< / span > < br > < span class = "line" > 7< / span > < br > < span class = "line" > 8< / span > < br > < span class = "line" > 9< / span > < br > < span class = "line" > 10< / span > < br > < span class = "line" > 11< / span > < br > < span class = "line" > 12< / span > < br > < span class = "line" > 13< / span > < br > < span class = "line" > 14< / span > < br > < span class = "line" > 15< / span > < br > < span class = "line" > 16< / span > < br > < span class = "line" > 17< / span > < br > < span class = "line" > 18< / span > < br > < span class = "line" > 19< / span > < br > < span class = "line" > 20< / span > < br > < span class = "line" > 21< / span > < br > < span class = "line" > 22< / span > < br > < span class = "line" > 23< / span > < br > < span class = "line" > 24< / span > < br > < span class = "line" > 25< / span > < br > < span class = "line" > 26< / span > < br > < span class = "line" > 27< / span > < br > < span class = "line" > 28< / span > < br > < span class = "line" > 29< / span > < br > < span class = "line" > 30< / span > < br > < span class = "line" > 31< / span > < br > < span class = "line" > 32< / span > < br > < span class = "line" > 33< / span > < br > < span class = "line" > 34< / span > < br > < span class = "line" > 35< / span > < br > < span class = "line" > 36< / span > < br > < span class = "line" > 37< / span > < br > < span class = "line" > 38< / span > < br > < span class = "line" > 39< / span > < br > < span class = "line" > 40< / span > < br > < span class = "line" > 41< / span > < br > < span class = "line" > 42< / span > < br > < span class = "line" > 43< / span > < br > < span class = "line" > 44< / span > < br > < span class = "line" > 45< / span > < br > < span class = "line" > 46< / span > < br > < span class = "line" > 47< / span > < br > < span class = "line" > 48< / span > < br > < span class = "line" > 49< / span > < br > < span class = "line" > 50< / span > < br > < span class = "line" > 51< / span > < br > < span class = "line" > 52< / span > < br > < span class = "line" > 53< / span > < br > < span class = "line" > 54< / span > < br > < span class = "line" > 55< / span > < br > < span class = "line" > 56< / span > < br > < span class = "line" > 57< / span > < br > < span class = "line" > 58< / span > < br > < span class = "line" > 59< / span > < br > < span class = "line" > 60< / span > < br > < span class = "line" > 61< / span > < br > < span class = "line" > 62< / span > < br > < span class = "line" > 63< / span > < br > < span class = "line" > 64< / span > < br > < span class = "line" > 65< / span > < br > < span class = "line" > 66< / span > < br > < span class = "line" > 67< / span > < br > < span class = "line" > 68< / span > < br > < span class = "line" > 69< / span > < br > < span class = "line" > 70< / span > < br > < span class = "line" > 71< / span > < br > < span class = "line" > 72< / span > < br > < span class = "line" > 73< / span > < br > < span class = "line" > 74< / span > < br > < span class = "line" > 75< / span > < br > < span class = "line" > 76< / span > < br > < span class = "line" > 77< / span > < br > < span class = "line" > 78< / span > < br > < span class = "line" > 79< / span > < br > < span class = "line" > 80< / span > < br > < span class = "line" > 81< / span > < br > < span class = "line" > 82< / span > < br > < span class = "line" > 83< / span > < br > < span class = "line" > 84< / span > < br > < span class = "line" > 85< / span > < br > < span class = "line" > 86< / span > < br > < span class = "line" > 87< / span > < br > < span class = "line" > 88< / span > < br > < span class = "line" > 89< / span > < br > < span class = "line" > 90< / span > < br > < span class = "line" > 91< / span > < br > < span class = "line" > 92< / span > < br > < span class = "line" > 93< / span > < br > < span class = "line" > 94< / span > < br > < span class = "line" > 95< / span > < br > < span class = "line" > 96< / span > < br > < span class = "line" > 97< / span > < br > < span class = "line" > 98< / span > < br > < span class = "line" > 99< / span > < br > < span class = "line" > 100< / span > < br > < span class = "line" > 101< / span > < br > < span class = "line" > 102< / span > < br > < span class = "line" > 103< / span > < br > < span class = "line" > 104< / span > < br > < span class = "line" > 105< / span > < br > < span class = "line" > 106< / span > < br > < span class = "line" > 107< / span > < br > < span class = "line" > 108< / span > < br > < span class = "line" > 109< / span > < br > < span class = "line" > 110< / span > < br > < span class = "line" > 111< / span > < br > < span class = "line" > 112< / span > < br > < span class = "line" > 113< / span > < br > < span class = "line" > 114< / span > < br > < span class = "line" > 115< / span > < br > < span class = "line" > 116< / span > < br > < span class = "line" > 117< / span > < br > < span class = "line" > 118< / span > < br > < span class = "line" > 119< / span > < br > < span class = "line" > 120< / span > < br > < span class = "line" > 121< / span > < br > < span class = "line" > 122< / span > < br > < span class = "line" > 123< / span > < br > < span class = "line" > 124< / span > < br > < span class = "line" > 125< / span > < br > < span class = "
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< h1 id = "二-MySql进阶" > < a href = "#二-MySql进阶" class = "headerlink" title = "二.MySql进阶" > < / a > 二.MySql进阶< / h1 > < h2 id = "1-存储引擎" > < a href = "#1-存储引擎" class = "headerlink" title = "1.存储引擎" > < / a > 1.存储引擎< / h2 > < h3 id = "1-1-MySql的体系结构" > < a href = "#1-1-MySql的体系结构" class = "headerlink" title = "1.1 MySql的体系结构" > < / a > 1.1 MySql的体系结构< / h3 > < p > < img src = "/pictures/image-20230916152706301.png" alt = "image-20230916152706301" > < / p >
< p > < img src = "/pictures/image-20230916152828704.png" alt = "image-20230916152828704" > < / p >
< h3 id = "1-2-存储引擎简介" > < a href = "#1-2-存储引擎简介" class = "headerlink" title = "1.2 存储引擎简介" > < / a > 1.2 存储引擎简介< / h3 > < p > < strong > 简介< / strong > < / p >
< p > / 查询数据等技术的实现方式 。存储引擎是基于表的，而不是 基于库的，所以存储引擎也可被称为表类型。我们可以在创建表的时候，来指定选择的存储引擎，如果 没有指定将自动选择默认的存储引擎。< / p >
< p > < strong > 查询一张数据库表的建表语句< / strong > < / p >
< figure class = "highlight sql" > < table > < tr > < td class = "gutter" > < pre > < span class = "line" > 1< / span > < br > < span class = "line" > 2< / span > < br > < / pre > < / td > < td class = "code" > < pre > < span class = "line" > < span class = "comment" > -- 查询建表语句< / span > < / span > < br > < span class = "line" > < span class = "keyword" > show< / span > < span class = "keyword" > create< / span > < span class = "keyword" > table< / span > book_info;< / span > < br > < / pre > < / td > < / tr > < / table > < / figure >
2023-09-22 21:57:28 +08:00
< p > < img src = "/pictures/image-20230916153448893.png" alt = "image-20230916153448893" > < / p >
< p > < strong > 建表的时候指定存储引擎的语句< / strong > < / p >
< p > < img src = "/pictures/image-20230916153931010.png" alt = "image-20230916153931010" > < / p >
< h3 id = "1-3-存储引擎特点" > < a href = "#1-3-存储引擎特点" class = "headerlink" title = "1.3 存储引擎特点" > < / a > 1.3 存储引擎特点< / h3 > < p > < img src = "/pictures/image-20230916154915533.png" alt = "image-20230916154915533" > < / p >
< p > < img src = "/pictures/image-20230916155113863.png" alt = "image-20230916155113863" > < / p >
< p > < img src = "/pictures/image-20230916155356755.png" alt = "image-20230916155356755" > < / p >
< p > < img src = "/pictures/image-20230916155525548.png" alt = "image-20230916155525548" > < / p >
< p > < strong > 存储引擎的区别< / strong > < / p >
< p > < img src = "/pictures/image-20230916155637133.png" alt = "image-20230916155637133" > < / p >
< h3 id = "1-4-存储引擎的选择" > < a href = "#1-4-存储引擎的选择" class = "headerlink" title = "1.4 存储引擎的选择" > < / a > 1.4 存储引擎的选择< / h3 > < p > < / p >
< ul >
< li > InnoDB: 是Mysql的默认存储引擎， ， < / li >
< li > MyISAM ： < / li >
< li > MEMORY： ， ， < / li >
< / ul >
< p > 一句话： < / p >
< h2 id = "2-索引" > < a href = "#2-索引" class = "headerlink" title = "2.索引" > < / a > 2.索引< / h2 > < h3 id = "2-1-索引概述" > < a href = "#2-1-索引概述" class = "headerlink" title = "2.1 索引概述" > < / a > 2.1 索引概述< / h3 > < h4 id = "2-1-1-介绍" > < a href = "#2-1-1-介绍" class = "headerlink" title = "2.1.1 介绍" > < / a > 2.1.1 介绍< / h4 > < p > （ ） < / p >
< h4 id = "2-1-2-演示" > < a href = "#2-1-2-演示" class = "headerlink" title = "2.1.2 演示" > < / a > 2.1.2 演示< / h4 > < p > 注：下面的二叉树并不是一个真实的索引结构，而是一个举例< / p >
< p > < img src = "/pictures/image-20230916150211012.png" alt = "image-20230916150211012" > < / p >
< h4 id = "2-1-3-优缺点" > < a href = "#2-1-3-优缺点" class = "headerlink" title = "2.1.3 优缺点" > < / a > 2.1.3 优缺点< / h4 > < p > < img src = "/pictures/image-20230916150430708.png" alt = "image-20230916150430708" > < / p >
< h3 id = "2-2-索引结构" > < a href = "#2-2-索引结构" class = "headerlink" title = "2.2 索引结构" > < / a > 2.2 索引结构< / h3 > < h4 id = "2-2-1-索引的数据结构有哪些" > < a href = "#2-2-1-索引的数据结构有哪些" class = "headerlink" title = "2.2.1 索引的数据结构有哪些" > < / a > 2.2.1 索引的数据结构有哪些< / h4 > < p > 默认的索引结构是B+树索引结构< / p >
< p > < img src = "/pictures/image-20230916161524219.png" alt = "image-20230916161524219" > < / p >
< p > < strong > 不同类型的存储引擎对不同的索引结构的支持情况< / strong > < / p >
< p > < img src = "/pictures/image-20230916161623546.png" alt = "image-20230916161623546" > < / p >
< h4 id = "2-2-2-B-树的索引数据结构" > < a href = "#2-2-2-B-树的索引数据结构" class = "headerlink" title = "2.2.2 B+树的索引数据结构" > < / a > 2.2.2 B+树的索引数据结构< / h4 > < p > < strong > 二叉树和红黑树的不足< / strong > < / p >
< p > < img src = "/pictures/image-20230916162305576.png" alt = "image-20230916162305576" > < / p >
< p > < strong > B树< / strong > < / p >
< p > < img src = "/pictures/image-20230916163234103.png" alt = "image-20230916163234103" > < / p >
< p > < strong > B+树< / strong > < / p >
< p > < img src = "/pictures/image-20230916164042303.png" alt = "image-20230916164042303" > < / p >
< p > < img src = "/pictures/image-20230916164314700.png" alt = "image-20230916164314700" > < / p >
< p > < strong > MySql中的B+树结构< / strong > < / p >
< p > < img src = "/pictures/image-20230916164500444.png" alt = "image-20230916164500444" > < / p >
< h4 id = "2-2-3-hash的索引数据结构" > < a href = "#2-2-3-hash的索引数据结构" class = "headerlink" title = "2.2.3 hash的索引数据结构" > < / a > 2.2.3 hash的索引数据结构< / h4 > < p > < img src = "/pictures/image-20230916164903702.png" alt = "image-20230916164903702" > < / p >
< p > < img src = "/pictures/image-20230916165007465.png" alt = "image-20230916165007465" > < / p >
< h4 id = "2-3-4-思考题" > < a href = "#2-3-4-思考题" class = "headerlink" title = "2.3.4 思考题" > < / a > 2.3.4 思考题< / h4 > < h4 id = "" > < a href = "#" class = "headerlink" title = "" > < / a > < img src = "/pictures/image-20230916165329434.png" alt = "image-20230916165329434" > < / h4 > < h3 id = "2-3-索引分类" > < a href = "#2-3-索引分类" class = "headerlink" title = "2.3 索引分类" > < / a > 2.3 索引分类< / h3 > < p > < img src = "/pictures/image-20230916165516779.png" alt = "image-20230916165516779" > < / p >
< p > < img src = "/pictures/image-20230916165647255.png" alt = "image-20230916165647255" > < / p >
< p > < img src = "/pictures/image-20230916170012664.png" alt = "image-20230916170012664" > < / p >
< p > 当我们要查询name值是Arm的数据的时候， ， （ ） < / p >
< p > < img src = "/pictures/image-20230916170421435.png" alt = "image-20230916170421435" > < / p >
< p > < strong > 思考题< / strong > < / p >
< p > < img src = "/pictures/image-20230916170537693.png" alt = "image-20230916170537693" > < / p >
< p > 第一条的执行效率高， （ ） < / p >
< h3 id = "2-4-索引语法" > < a href = "#2-4-索引语法" class = "headerlink" title = "2.4 索引语法" > < / a > 2.4 索引语法< / h3 > < p > < strong > 创建|查看|删除语法< / strong > < / p >
< p > < img src = "/pictures/image-20230917091746406.png" alt = "image-20230917091746406" > < / p >
< p > < strong > 举例< / strong > < / p >
< p > < img src = "/pictures/image-20230917093020287.png" alt = "image-20230917093020287" > < / p >
< h3 id = "2-5-SQL性能分析" > < a href = "#2-5-SQL性能分析" class = "headerlink" title = "2.5 SQL性能分析" > < / a > 2.5 SQL性能分析< / h3 > < h4 id = "2-5-1-SQL执行频率" > < a href = "#2-5-1-SQL执行频率" class = "headerlink" title = "2.5.1 SQL执行频率" > < / a > 2.5.1 SQL执行频率< / h4 > < p > < img src = "/pictures/image-20230917093634100.png" alt = "image-20230917093634100" > < / p >
< figure class = "highlight sql" > < table > < tr > < td class = "gutter" > < pre > < span class = "line" > 1< / span > < br > < span class = "line" > 2< / span > < br > < / pre > < / td > < td class = "code" > < pre > < span class = "line" > < span class = "comment" > -- 查看系统的状态信息< / span > < / span > < br > < span class = "line" > < span class = "keyword" > show< / span > < span class = "keyword" > global< / span > status < span class = "keyword" > like< / span > < span class = "string" > ' Com_______' < / span > ;< / span > < br > < / pre > < / td > < / tr > < / table > < / figure >
< h4 id = "2-5-2-慢查询日志" > < a href = "#2-5-2-慢查询日志" class = "headerlink" title = "2.5.2 慢查询日志" > < / a > 2.5.2 慢查询日志< / h4 > < p > < img src = "/pictures/image-20230917094314803.png" alt = "image-20230917094314803" > < / p >
< figure class = "highlight sql" > < table > < tr > < td class = "gutter" > < pre > < span class = "line" > 1< / span > < br > < span class = "line" > 2< / span > < br > < / pre > < / td > < td class = "code" > < pre > < span class = "line" > < span class = "comment" > -- 查询慢查询日志是否开启< / span > < / span > < br > < span class = "line" > < span class = "keyword" > show< / span > variables < span class = "keyword" > like< / span > < span class = "string" > ' slow_query_log' < / span > ;< / span > < br > < / pre > < / td > < / tr > < / table > < / figure >
< h4 id = "2-5-3-profile详情" > < a href = "#2-5-3-profile详情" class = "headerlink" title = "2.5.3 profile详情" > < / a > 2.5.3 profile详情< / h4 > < p > < img src = "/pictures/image-20230917095232011.png" alt = "image-20230917095232011" > < / p >
< figure class = "highlight sql" > < table > < tr > < td class = "gutter" > < pre > < span class = "line" > 1< / span > < br > < span class = "line" > 2< / span > < br > < span class = "line" > 3< / span > < br > < span class = "line" > 4< / span > < br > < span class = "line" > 5< / span > < br > < span class = "line" > 6< / span > < br > < span class = "line" > 7< / span > < br > < span class = "line" > 8< / span > < br > < / pre > < / td > < td class = "code" > < pre > < span class = "line" > < span class = "comment" > -- 是否支持profile详情功能< / span > < / span > < br > < span class = "line" > < span class = "keyword" > select< / span > @< span class = "variable" > @have_profiling< / span > ;< / span > < br > < span class = "line" > < / span > < br > < span class = "line" > < span class = "comment" > -- 查看是否开启该功能< / span > < / span > < br > < span class = "line" > < span class = "keyword" > select< / span > @< span class = "variable" > @profiling< / span > ;< / span > < br > < span class = "line" > < / span > < br > < span class = "line" > < span class = "comment" > -- 开启profile< / span > < / span > < br > < span class = "line" > < span class = "keyword" > set< / span > profiling < span class = "operator" > =< / span > < span class = "number" > 1< / span > ;< / span > < br > < / pre > < / td > < / tr > < / table > < / figure >
< p > < img src = "/pictures/image-20230917095320953.png" alt = "image-20230917095320953" > < / p >
< h4 id = "2-5-4-explain执行计划" > < a href = "#2-5-4-explain执行计划" class = "headerlink" title = "2.5.4 explain执行计划" > < / a > 2.5.4 explain执行计划< / h4 > < p > < img src = "/pictures/image-20230917095911304.png" alt = "image-20230917095911304" > < / p >
< p > < img src = "/pictures/image-20230917101205097.png" alt = "image-20230917101205097" > < / p >
< p > < img src = "/pictures/image-20230917101337147.png" alt = "image-20230917101337147" > < / p >
< h3 id = "2-6-索引使用" > < a href = "#2-6-索引使用" class = "headerlink" title = "2.6 索引使用" > < / a > 2.6 索引使用< / h3 > < h4 id = "2-6-1-验证索引效率" > < a href = "#2-6-1-验证索引效率" class = "headerlink" title = "2.6.1 验证索引效率" > < / a > 2.6.1 验证索引效率< / h4 > < p > < img src = "/pictures/image-20230917141334774.png" alt = "image-20230917141334774" > < / p >
< p > 现在有一个有着10000000数据的表（ ） ， ， ， ， ， < / p >
< h4 id = "2-6-2-最左前缀法则" > < a href = "#2-6-2-最左前缀法则" class = "headerlink" title = "2.6.2 最左前缀法则" > < / a > 2.6.2 最左前缀法则< / h4 > < p > < img src = "/pictures/image-20230917142410276.png" alt = "image-20230917142410276" > < / p >
< p > < img src = "/pictures/image-20230917142707646.png" alt = "image-20230917142707646" > < / p >
< h4 id = "2-6-3-索引失效的情况" > < a href = "#2-6-3-索引失效的情况" class = "headerlink" title = "2.6.3 索引失效的情况" > < / a > 2.6.3 索引失效的情况< / h4 > < p > < img src = "/pictures/image-20230917142948227.png" alt = "image-20230917142948227" > < / p >
< p > < img src = "/pictures/image-20230917143143047.png" alt = "image-20230917143143047" > < / p >
< p > < img src = "/pictures/image-20230917143421975.png" alt = "image-20230917143421975" > < / p >
< p > < img src = "/pictures/image-20230917143842497.png" alt = "image-20230917143842497" > < / p >
< p > < img src = "/pictures/image-20230917144459567.png" alt = "image-20230917144459567" > < / p >
< h4 id = "2-6-4-SQL提示" > < a href = "#2-6-4-SQL提示" class = "headerlink" title = "2.6.4 SQL提示" > < / a > 2.6.4 SQL提示< / h4 > < p > < img src = "/pictures/image-20230917145046280.png" alt = "image-20230917145046280" > < / p >
< h4 id = "2-6-5-覆盖索引" > < a href = "#2-6-5-覆盖索引" class = "headerlink" title = "2.6.5 覆盖索引" > < / a > 2.6.5 覆盖索引< / h4 > < p > < img src = "/pictures/image-20230917145643194.png" alt = "image-20230917145643194" > < / p >
< h4 id = "2-6-6-前缀索引" > < a href = "#2-6-6-前缀索引" class = "headerlink" title = "2.6.6 前缀索引" > < / a > 2.6.6 前缀索引< / h4 > < p > < img src = "/pictures/image-20230917153757773.png" alt = "image-20230917153757773" > < / p >
< p > < img src = "/pictures/image-20230917154300147.png" alt = "image-20230917154300147" > < / p >
< h4 id = "2-6-7-单例索引与联合索引的选择问题" > < a href = "#2-6-7-单例索引与联合索引的选择问题" class = "headerlink" title = "2.6.7 单例索引与联合索引的选择问题" > < / a > 2.6.7 单例索引与联合索引的选择问题< / h4 > < p > < img src = "/pictures/image-20230917155017641.png" alt = "image-20230917155017641" > < / p >
< p > < img src = "/pictures/image-20230917155223679.png" alt = "image-20230917155223679" > < / p >
< h3 id = "2-7-索引设计原则" > < a href = "#2-7-索引设计原则" class = "headerlink" title = "2.7 索引设计原则" > < / a > 2.7 索引设计原则< / h3 > < p > < img src = "/pictures/image-20230917155748055.png" alt = "image-20230917155748055" > < / p >
< h2 id = "3-SQL优化" > < a href = "#3-SQL优化" class = "headerlink" title = "3.SQL优化" > < / a > 3.SQL优化< / h2 > < h3 id = "3-1-插入数据的优化" > < a href = "#3-1-插入数据的优化" class = "headerlink" title = "3.1 插入数据的优化" > < / a > 3.1 插入数据的优化< / h3 > < p > < img src = "/pictures/image-20230917181618942.png" alt = "image-20230917181618942" > < / p >
< p > < img src = "/pictures/image-20230917181842030.png" alt = "image-20230917181842030" > < / p >
< p > 100万的数据如果使用insert插入的话需要10分钟左右， ， < / p >
< h3 id = "3-2-主键优化" > < a href = "#3-2-主键优化" class = "headerlink" title = "3.2 主键优化" > < / a > 3.2 主键优化< / h3 > < p > < img src = "/pictures/image-20230917205500523.png" alt = "image-20230917205500523" > < / p >
< p > < img src = "/pictures/image-20230917205636137.png" alt = "image-20230917205636137" > < / p >
< p > < img src = "/pictures/image-20230917205833596.png" alt = "image-20230917205833596" > < / p >
< p > < img src = "/pictures/image-20230917210112389.png" alt = "image-20230917210112389" > < / p >
< p > < img src = "/pictures/image-20230917210303469.png" alt = "image-20230917210303469" > < / p >
< h3 id = "3-3-order-by优化" > < a href = "#3-3-order-by优化" class = "headerlink" title = "3.3 order by优化" > < / a > 3.3 order by优化< / h3 > < p > < img src = "/pictures/image-20230917210730392.png" alt = "image-20230917210730392" > < / p >
< p > < img src = "/pictures/image-20230917211254167.png" alt = "image-20230917211254167" > < / p >
< p > < img src = "/pictures/image-20230917210616858.png" alt = "image-20230917210616858" > < / p >
< p > < img src = "/pictures/image-20230917211543109.png" alt = "image-20230917211543109" > < / p >
< h3 id = "3-4-group-by优化" > < a href = "#3-4-group-by优化" class = "headerlink" title = "3.4 group by优化" > < / a > 3.4 group by优化< / h3 > < p > < img src = "/pictures/image-20230917212026101.png" alt = "image-20230917212026101" > < / p >
< h3 id = "3-5-limit优化" > < a href = "#3-5-limit优化" class = "headerlink" title = "3.5 limit优化" > < / a > 3.5 limit优化< / h3 > < p > < img src = "/pictures/image-20230917212530539.png" alt = "image-20230917212530539" > < / p >
< h3 id = "3-6-count优化" > < a href = "#3-6-count优化" class = "headerlink" title = "3.6 count优化" > < / a > 3.6 count优化< / h3 > < p > < img src = "/pictures/image-20230917212709489.png" alt = "image-20230917212709489" > < / p >
< p > < img src = "/pictures/image-20230917213029734.png" alt = "image-20230917213029734" > < / p >
< p > < img src = "/pictures/image-20230917213316193.png" alt = "image-20230917213316193" > < / p >
< h3 id = "3-7-update优化" > < a href = "#3-7-update优化" class = "headerlink" title = "3.7 update优化" > < / a > 3.7 update优化< / h3 > < p > < img src = "/pictures/image-20230917213859581.png" alt = "image-20230917213859581" > < / p >
< h3 id = "3-8-总结" > < a href = "#3-8-总结" class = "headerlink" title = "3.8 总结" > < / a > 3.8 总结< / h3 > < p > < img src = "/pictures/image-20230917214424722.png" alt = "image-20230917214424722" > < / p >
2023-10-06 19:27:36 +08:00
< h2 id = "4-视图-存储过程-触发器" > < a href = "#4-视图-存储过程-触发器" class = "headerlink" title = "4.视图/存储过程/触发器" > < / a > 4.视图/ 存储过程/ 触发器< / h2 > < h3 id = "4-1-视图" > < a href = "#4-1-视图" class = "headerlink" title = "4.1 视图" > < / a > 4.1 视图< / h3 > < h4 id = "4-1-1-视图介绍" > < a href = "#4-1-1-视图介绍" class = "headerlink" title = "4.1.1 视图介绍" > < / a > 4.1.1 视图介绍< / h4 > < p > （ ） ， ， ， ， ， < / p >
< h4 id = "4-1-2-语法" > < a href = "#4-1-2-语法" class = "headerlink" title = "4.1.2 语法" > < / a > 4.1.2 语法< / h4 > < p > < strong > 创建< / strong > < / p >
< figure class = "highlight sql" > < table > < tr > < td class = "gutter" > < pre > < span class = "line" > 1< / span > < br > < / pre > < / td > < td class = "code" > < pre > < span class = "line" > < span class = "keyword" > CREATE< / span > [< span class = "keyword" > OR< / span > REPLACE] < span class = "keyword" > VIEW< / span > 视图名称[(列名列表)] < span class = "keyword" > AS< / span > < span class = "keyword" > SELECT< / span > 语句 [ < span class = "keyword" > WITH< / span > [< span class = "keyword" > CASCADED< / span > < span class = "operator" > |< / span > < span class = "keyword" > LOCAL< / span > ] < span class = "keyword" > CHECK< / span > OPTION ]< / span > < br > < / pre > < / td > < / tr > < / table > < / figure >
< p > < strong > 查询< / strong > < / p >
< figure class = "highlight sql" > < table > < tr > < td class = "gutter" > < pre > < span class = "line" > 1< / span > < br > < span class = "line" > 2< / span > < br > < / pre > < / td > < td class = "code" > < pre > < span class = "line" > 查看创建视图语句：< span class = "keyword" > SHOW< / span > < span class = "keyword" > CREATE< / span > < span class = "keyword" > VIEW< / span > 视图名称;< / span > < br > < span class = "line" > 查看视图数据：< span class = "keyword" > SELECT< / span > < span class = "operator" > *< / span > < span class = "keyword" > FROM< / span > 视图名称 ...... ;< / span > < br > < / pre > < / td > < / tr > < / table > < / figure >
< p > < strong > 修改< / strong > < / p >
< figure class = "highlight sql" > < table > < tr > < td class = "gutter" > < pre > < span class = "line" > 1< / span > < br > < span class = "line" > 2< / span > < br > < / pre > < / td > < td class = "code" > < pre > < span class = "line" > 方式一：< span class = "keyword" > CREATE< / span > [< span class = "keyword" > OR< / span > REPLACE] < span class = "keyword" > VIEW< / span > 视图名称[(列名列表)] < span class = "keyword" > AS< / span > < span class = "keyword" > SELECT< / span > 语句 [ < span class = "keyword" > WITH< / span > [ < span class = "keyword" > CASCADED< / span > < span class = "operator" > |< / span > < span class = "keyword" > LOCAL< / span > ] < span class = "keyword" > CHECK< / span > OPTION ]< / span > < br > < span class = "line" > 方式二：< span class = "keyword" > ALTER< / span > < span class = "keyword" > VIEW< / span > 视图名称[(列名列表)] < span class = "keyword" > AS< / span > < span class = "keyword" > SELECT< / span > 语句 [ < span class = "keyword" > WITH< / span > [ < span class = "keyword" > CASCADED< / span > < span class = "operator" > |< / span > < span class = "keyword" > LOCAL< / span > ] < span class = "keyword" > CHECK< / span > OPTION ]< / span > < br > < / pre > < / td > < / tr > < / table > < / figure >
< p > < strong > 删除< / strong > < / p >
< figure class = "highlight sql" > < table > < tr > < td class = "gutter" > < pre > < span class = "line" > 1< / span > < br > < / pre > < / td > < td class = "code" > < pre > < span class = "line" > < span class = "keyword" > DROP< / span > < span class = "keyword" > VIEW< / span > [IF < span class = "keyword" > EXISTS< / span > ] 视图名称 [,视图名称] ...< / span > < br > < / pre > < / td > < / tr > < / table > < / figure >
< p > < strong > 演示示例< / strong > < / p >
< figure class = "highlight sql" > < table > < tr > < td class = "gutter" > < pre > < span class = "line" > 1< / span > < br > < span class = "line" > 2< / span > < br > < span class = "line" > 3< / span > < br > < span class = "line" > 4< / span > < br > < span class = "line" > 5< / span > < br > < span class = "line" > 6< / span > < br > < span class = "line" > 7< / span > < br > < span class = "line" > 8< / span > < br > < span class = "line" > 9< / span > < br > < span class = "line" > 10< / span > < br > < span class = "line" > 11< / span > < br > < span class = "line" > 12< / span > < br > < span class = "line" > 13< / span > < br > < span class = "line" > 14< / span > < br > < span class = "line" > 15< / span > < br > < span class = "line" > 16< / span > < br > < span class = "line" > 17< / span > < br > < span class = "line" > 18< / span > < br > < span class = "line" > 19< / span > < br > < span class = "line" > 20< / span > < br > < span class = "line" > 21< / span > < br > < span class = "line" > 22< / span > < br > < span class = "line" > 23< / span > < br > < span class = "line" > 24< / span > < br > < span class = "line" > 25< / span > < br > < span class = "line" > 26< / span > < br > < / pre > < / td > < td class = "code" > < pre > < span class = "line" > < span class = "comment" > -- 视图< / span > < / span > < br > < span class = "line" > < span class = "comment" > -- 创建视图< / span > < / span > < br > < span class = "line" > < span class = "keyword" > create< / span > < span class = "keyword" > or< / span > replace < span class = "keyword" > view< / span > stu_v_1 < span class = "keyword" > as< / span > < span class = "keyword" > select< / span > id, name < span class = "keyword" > from< / span > student < span class = "keyword" > where< / span > id < span class = "operator" > < =< / span > < span class = "number" > 10< / span > ;< / span > < br > < span class = "line" > < / span > < br > < span class = "line" > < span class = "comment" > -- 查看创建视图的语句< / span > < / span > < br > < span class = "line" > < span class = "keyword" > show< / span > < span class = "keyword" > create< / span > < span class = "keyword" > view< / span > stu_v_1;< / span > < br > < span class = "line" > < / span > < br > < span class = "line" > < span class = "comment" > -- 查看视图数据< / span > < / span > < br > < span class = "line" > < span class = "keyword" > select< / span > < span class = "operator" > *< / span > < span class = "keyword" > from< / span > stu_v_1;< / span > < br > < span class = "line" > < span class = "comment" > -- 也可以加上条件< / span > < / span > < br > < span class = "line" > < span class = "keyword" > select< / span > < span class = "operator" > *< / span > < span class = "keyword" > from< / span > stu_v_1 < span class = "keyword" > where< / span > id < span class = "operator" > =< / span > < span class = "number" > 1< / span > ;< / span > < br > < span class = "line" > < / span > < br > < span class = "line" > < span class = "comment" > -- 修改视图的方式(or replace可以实现修改效果)< / span > < / span > < br > < span class = "line" > < span class = "comment" > -- 方式一< / span > < / span > < br > < span class = "line" > < span class = "keyword" > create< / span > < span class = "keyword" > or< / span > replace < span class = "keyword" > view< / span > stu_v_1 < span class = "keyword" > as< / span > < span class = "keyword" > select< / span > id, name, < span class = "keyword" > no< / span > < span class = "keyword" > from< / span > student < span class = "keyword" > where< / span > id < span class = "operator" > < =< / span > < span class = "number" > 10< / span > ;< / span > < br > < span class = "line" > < span class = "comment" > -- 方式二< / span > < / span > < br > < span class = "line" > < span class = "keyword" > alter< / span > < span class = "keyword" > view< / span > stu_v_1 < span class = "keyword" > as< / span > < span class = "keyword" > select< / span > id, name < span class = "keyword" > from< / span > student < span class = "keyword" > where< / span > id < span class = "operator" > < =< / span > < span class = "number" > 10< / span > ;< / span > < br > < span class = "line" > < / span > < br > < span class = "line" > < span class = "comment" > -- 删除视图< / span > < / span > < br > < span class = "line" > < span class = "keyword" > drop< / span > < span class = "keyword" > view< / span > if < span class = "keyword" > exists< / span > stu_v_1;< / span > < br > < span class = "line" > < / span > < br > < span class = "line" > < span class = "comment" > -- 通过视图实现插入操作< / span > < / span > < br > < span class = "line" > < span class = "keyword" > create< / span > < span class = "keyword" > or< / span > replace < span class = "keyword" > view< / span > stu_v_1 < span class = "keyword" > as< / span > < span class = "keyword" > select< / span > id, name < span class = "keyword" > from< / span > student < span class = "keyword" > where< / span > id < span class = "operator" > < =< / span > < span class = "number" > 20< / span > ;< / span > < br > < span class = "line" > < / span > < br > < span class = "line" > < span
< h4 id = "4-1-3-检查选项" > < a href = "#4-1-3-检查选项" class = "headerlink" title = "4.1.3 检查选项" > < / a > 4.1.3 检查选项< / h4 > < p > ， ， ， ， ， ， ， ： ， < / p >
< p > < strong > 1.CASCADED< / strong > 级联< / p >
< p > ， ， ， ， ， < / p >
< p > < img src = "/pictures/image-20231006182938266.png" alt = "image-20231006182938266" > < / p >
< p > < strong > 2.LOCAL< / strong > 本地< / p >
< p > ， ， ， ， ， < / p >
< p > < img src = "/pictures/image-20231006183051143.png" alt = "image-20231006183051143" > < / p >
< figure class = "highlight sql" > < table > < tr > < td class = "gutter" > < pre > < span class = "line" > 1< / span > < br > < span class = "line" > 2< / span > < br > < span class = "line" > 3< / span > < br > < span class = "line" > 4< / span > < br > < span class = "line" > 5< / span > < br > < span class = "line" > 6< / span > < br > < span class = "line" > 7< / span > < br > < span class = "line" > 8< / span > < br > < span class = "line" > 9< / span > < br > < span class = "line" > 10< / span > < br > < span class = "line" > 11< / span > < br > < span class = "line" > 12< / span > < br > < span class = "line" > 13< / span > < br > < span class = "line" > 14< / span > < br > < span class = "line" > 15< / span > < br > < / pre > < / td > < td class = "code" > < pre > < span class = "line" > < span class = "comment" > -- 检查选项< / span > < / span > < br > < span class = "line" > < span class = "comment" > -- 添加了检查选项，在插入数据的时候会检查插入的数据是否满足视图创建的条件(创建语句为create or replace view stu_v_1 as select id, name from student where id < = 20;此时插入的数据id要< =20,否则报错)< / span > < / span > < br > < span class = "line" > < span class = "comment" > -- cascaded:插入时会检查是否满足当前视图和依赖的视图的条件< / span > < / span > < br > < span class = "line" > < span class = "keyword" > create< / span > < span class = "keyword" > or< / span > replace < span class = "keyword" > view< / span > stu_v_1 < span class = "keyword" > as< / span > < span class = "keyword" > select< / span > id, name < span class = "keyword" > from< / span > student < span class = "keyword" > where< / span > id < span class = "operator" > < =< / span > < span class = "number" > 20< / span > < span class = "keyword" > with< / span > < span class = "keyword" > cascaded< / span > < span class = "keyword" > check< / span > option ;< / span > < br > < span class = "line" > < / span > < br > < span class = "line" > < span class = "comment" > -- local:插入时会检查是否满足当前视图和依赖的视图(定义了检查选项的视图)的条件< / span > < / span > < br > < span class = "line" > < span class = "keyword" > create< / span > < span class = "keyword" > or< / span > replace < span class = "keyword" > view< / span > stu_v_1 < span class = "keyword" > as< / span > < span class = "keyword" > select< / span > id, name < span class = "keyword" > from< / span > student < span class = "keyword" > where< / span > id < span class = "operator" > < =< / span > < span class = "number" > 20< / span > < span class = "keyword" > with< / span > < span class = "keyword" > local< / span > < span class = "keyword" > check< / span > option ;< / span > < br > < span class = "line" > < / span > < br > < span class = "line" > < span class = "comment" > -- local和cascaded的区别:< / span > < / span > < br > < span class = "line" > < span class = "comment" > -- local:v2依赖了v1,只有v1也加上了with local check option检查选项,在v2插入数据的时候才会检查v1的条件< / span > < / span > < br > < span class = "line" > < span class = "comment" > -- cascaded:v2依赖了v1,不管v1有没有加上检查选项,在v2插入数据时都会检查v1的条件< / span > < / span > < br > < span class = "line" > < / span > < br > < span class = "line" > < span class = "comment" > -- 重点< / span > < / span > < br > < span class = "line" > < span class = "comment" > -- 1.加不加检查选项的区别< / span > < / span > < br > < span class = "line" > < span class = "comment" > -- 2.with cascaded check option和with local check option的区别< / span > < / span > < br > < / pre > < / td > < / tr > < / table > < / figure >
< h4 id = "4-1-4-视图更新" > < a href = "#4-1-4-视图更新" class = "headerlink" title = "4.1.4 视图更新" > < / a > 4.1.4 视图更新< / h4 > < p > 要使视图可更新，视图中的行与基础表中的行之间必须存在一对一的关系。如果视图包含以下任何一项，则该视图不可更新：< / p >
< p > A. 聚合函数或窗口函数（ < / p >
< p > B. DISTINCT< / p >
< p > C. GROUP BY< / p >
< p > D. HAVING< / p >
< p > E. UNION 或者 UNION ALL< / p >
< p > < img src = "/pictures/image-20231006184725321.png" alt = "image-20231006184725321" > < / p >
< h4 id = "4-1-5-视图作用" > < a href = "#4-1-5-视图作用" class = "headerlink" title = "4.1.5 视图作用" > < / a > 4.1.5 视图作用< / h4 > < p > < img src = "/pictures/image-20231006185121986.png" alt = "image-20231006185121986" > < / p >
< h4 id = "4-1-6-视图案例" > < a href = "#4-1-6-视图案例" class = "headerlink" title = "4.1.6 视图案例" > < / a > 4.1.6 视图案例< / h4 > < p > tb_user表结构以及sql语句< / p >
< figure class = "highlight sql" > < table > < tr > < td class = "gutter" > < pre > < span class = "line" > 1< / span > < br > < span class = "line" > 2< / span > < br > < span class = "line" > 3< / span > < br > < span class = "line" > 4< / span > < br > < span class = "line" > 5< / span > < br > < span class = "line" > 6< / span > < br > < span class = "line" > 7< / span > < br > < span class = "line" > 8< / span > < br > < span class = "line" > 9< / span > < br > < span class = "line" > 10< / span > < br > < span class = "line" > 11< / span > < br > < span class = "line" > 12< / span > < br > < span class = "line" > 13< / span > < br > < span class = "line" > 14< / span > < br > < span class = "line" > 15< / span > < br > < span class = "line" > 16< / span > < br > < span class = "line" > 17< / span > < br > < span class = "line" > 18< / span > < br > < span class = "line" > 19< / span > < br > < span class = "line" > 20< / span > < br > < span class = "line" > 21< / span > < br > < span class = "line" > 22< / span > < br > < span class = "line" > 23< / span > < br > < span class = "line" > 24< / span > < br > < span class = "line" > 25< / span > < br > < span class = "line" > 26< / span > < br > < span class = "line" > 27< / span > < br > < span class = "line" > 28< / span > < br > < span class = "line" > 29< / span > < br > < span class = "line" > 30< / span > < br > < span class = "line" > 31< / span > < br > < span class = "line" > 32< / span > < br > < span class = "line" > 33< / span > < br > < span class = "line" > 34< / span > < br > < span class = "line" > 35< / span > < br > < span class = "line" > 36< / span > < br > < span class = "line" > 37< / span > < br > < / pre > < / td > < td class = "code" > < pre > < span class = "line" > < span class = "keyword" > create< / span > < span class = "keyword" > table< / span > tb_user(< / span > < br > < span class = "line" > id < span class = "type" > int< / span > < span class = "keyword" > primary< / span > key auto_increment comment < span class = "string" > ' 主键' < / span > ,< / span > < br > < span class = "line" > name < span class = "type" > varchar< / span > (< span class = "number" > 50< / span > ) < span class = "keyword" > not< / span > < span class = "keyword" > null< / span > comment < span class = "string" > ' 用户名' < / span > ,< / span > < br > < span class = "line" > phone < span class = "type" > varchar< / span > (< span class = "number" > 11< / span > ) < span class = "keyword" > not< / span > < span class = "keyword" > null< / span > comment < span class = "string" > ' 手机号' < / span > ,< / span > < br > < span class = "line" > email < span class = "type" > varchar< / span > (< span class = "number" > 100< / span > ) comment < span class = "string" > ' 邮箱' < / span > ,< / span > < br > < span class = "line" > profession < span class = "type" > varchar< / span > (< span class = "number" > 11< / span > ) comment < span class = "string" > ' 专业' < / span > ,< / span > < br > < span class = "line" > age tinyint unsigned comment < span class = "string" > ' 年龄' < / span > ,< / span > < br > < span class = "line" > gender < span class = "type" > char< / span > (< span class = "number" > 1< / span > ) comment < span class = "string" > ' 性别 , 1: 男, 2: 女' < / span > ,< / span > < br > < span class = "line" > status < span class = "type" > char< / span > (< span class = "number" > 1< / span > ) comment < span class = "string" > ' 状态' < / span > ,< / span > < br > < span class = "line" > createtime datetime comment < span class = "string" > ' 创建时间' < / span > < / span > < br > < span class = "line" > ) comment < span class = "string" > ' 系统用户表' < / span > ;< / span > < br > < span class = "line" > < / span > < br > < span class = "line" > < / span > < br > < span class = "line" > < span class = "keyword" > INSERT< / span > < span class = "keyword" > INTO< / span > itcast.tb_user (name, phone, email, profession, age, gender, status, createtime) < span class = "keyword" > VALUES< / span > (< span class = "string" > ' 吕布' < / span > , < span class = "string" > ' 17799990000' < / span > , < span class = "string" > ' lvbu666@163.com' < / span > , < span class = "string" > ' 软件工程' < / span > , < span class = "number" > 23< / span > , < span class = "string" > ' 1' < / span > , < span class = "string" > ' 6' < / span > , < span class = "string" > ' 2001-02-02 00:00:00' < / span > );< / span > < br > < span class = "line" > < span class = "keyword" > INSERT< / span > < span class = "keyword" > INTO< / span > itcast.tb_user (name, phone, email, profession, age, gender, status, createtime) < span class = "keyword" > VALUES< / span > (< span class = "string" > ' 曹操' < / span > , < span class = "string" > ' 17799990001' < / span > , < span class = "string" > ' caocao666@qq.com' < / span > , < span class = "string" > ' 通讯工程' < / span > , < span class = "number" > 33< / span > ,
< p > 案例< / p >
< figure class = "highlight sql" > < table > < tr > < td class = "gutter" > < pre > < span class = "line" > 1< / span > < br > < span class = "line" > 2< / span > < br > < span class = "line" > 3< / span > < br > < span class = "line" > 4< / span > < br > < span class = "line" > 5< / span > < br > < span class = "line" > 6< / span > < br > < span class = "line" > 7< / span > < br > < / pre > < / td > < td class = "code" > < pre > < span class = "line" > < span class = "comment" > -- 视图案例< / span > < / span > < br > < span class = "line" > < span class = "comment" > -- 为了保证数据库表的安全性， ， ， < / span > < / span > < br > < span class = "line" > < span class = "keyword" > create< / span > < span class = "keyword" > view< / span > tb_user_view < span class = "keyword" > as< / span > < span class = "keyword" > select< / span > id, name, profession, age, gender, status, createtime < span class = "keyword" > from< / span > tb_user;< / span > < br > < span class = "line" > < span class = "keyword" > select< / span > < span class = "operator" > *< / span > < span class = "keyword" > from< / span > tb_user_view;< / span > < br > < span class = "line" > < / span > < br > < span class = "line" > < span class = "comment" > -- 查询每个学生所选修的课程（三张表联查），这个功能在很多的业务中都有使用到，为了简化操作，定义一个视图< / span > < / span > < br > < span class = "line" > < span class = "keyword" > create< / span > < span class = "keyword" > view< / span > tb_stu_course_view < span class = "keyword" > as< / span > < span class = "keyword" > select< / span > s.name student_name,s.no,c.name course_name < span class = "keyword" > from< / span > student s, course c, student_course sc < span class = "keyword" > where< / span > s.id < span class = "operator" > =< / span > sc.studentid < span class = "keyword" > and< / span > c.id < span class = "operator" > =< / span > sc.courseid;< / span > < br > < / pre > < / td > < / tr > < / table > < / figure >
< h3 id = "4-2-存储过程" > < a href = "#4-2-存储过程" class = "headerlink" title = "4.2 存储过程" > < / a > 4.2 存储过程< / h3 > < h4 id = "4-2-1-介绍" > < a href = "#4-2-1-介绍" class = "headerlink" title = "4.2.1 介绍" > < / a > 4.2.1 介绍< / h4 > < p > < img src = "/pictures/image-20231006190705216.png" alt = "image-20231006190705216" > < / p >
< p > < img src = "/pictures/image-20231006190743209.png" alt = "image-20231006190743209" > < / p >
< h4 id = "4-2-2-基本语法" > < a href = "#4-2-2-基本语法" class = "headerlink" title = "4.2.2 基本语法" > < / a > 4.2.2 基本语法< / h4 > < p > < strong > 创建< / strong > < / p >
< figure class = "highlight sql" > < table > < tr > < td class = "gutter" > < pre > < span class = "line" > 1< / span > < br > < span class = "line" > 2< / span > < br > < span class = "line" > 3< / span > < br > < span class = "line" > 4< / span > < br > < / pre > < / td > < td class = "code" > < pre > < span class = "line" > < span class = "keyword" > CREATE< / span > < span class = "keyword" > PROCEDURE< / span > 存储过程名称 ([ 参数列表 ])< / span > < br > < span class = "line" > < span class = "keyword" > BEGIN< / span > < / span > < br > < span class = "line" > < span class = "comment" > -- SQL语句< / span > < / span > < br > < span class = "line" > < span class = "keyword" > END< / span > ;< / span > < br > < / pre > < / td > < / tr > < / table > < / figure >
< p > < strong > 调用< / strong > < / p >
< figure class = "highlight sql" > < table > < tr > < td class = "gutter" > < pre > < span class = "line" > 1< / span > < br > < / pre > < / td > < td class = "code" > < pre > < span class = "line" > < span class = "keyword" > CALL< / span > 名称 ([ 参数 ]);< / span > < br > < / pre > < / td > < / tr > < / table > < / figure >
< p > < strong > 查看< / strong > < / p >
< figure class = "highlight sql" > < table > < tr > < td class = "gutter" > < pre > < span class = "line" > 1< / span > < br > < span class = "line" > 2< / span > < br > < span class = "line" > 3< / span > < br > < / pre > < / td > < td class = "code" > < pre > < span class = "line" > < span class = "keyword" > SELECT< / span > < span class = "operator" > *< / span > < span class = "keyword" > FROM< / span > INFORMATION_SCHEMA.ROUTINES < span class = "keyword" > WHERE< / span > ROUTINE_SCHEMA < span class = "operator" > =< / span > < span class = "string" > ' xxx' < / span > ; < span class = "comment" > -- 查询指定数据库的存储过程及状态信息< / span > < / span > < br > < span class = "line" > < / span > < br > < span class = "line" > < span class = "keyword" > SHOW< / span > < span class = "keyword" > CREATE< / span > < span class = "keyword" > PROCEDURE< / span > 存储过程名称 ; < span class = "comment" > -- 查询某个存储过程的定义< / span > < / span > < br > < / pre > < / td > < / tr > < / table > < / figure >
< p > < strong > 删除< / strong > < / p >
< figure class = "highlight sql" > < table > < tr > < td class = "gutter" > < pre > < span class = "line" > 1< / span > < br > < / pre > < / td > < td class = "code" > < pre > < span class = "line" > < span class = "keyword" > DROP< / span > < span class = "keyword" > PROCEDURE< / span > [ IF < span class = "keyword" > EXISTS< / span > ] 存储过程名称 ； < / span > < br > < / pre > < / td > < / tr > < / table > < / figure >
< blockquote >
< p > 注意:< br > 在命令行中， ， < / p >
< / blockquote >
< p > < strong > 演示示例< / strong > < / p >
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< figure class = "highlight sql" > < table > < tr > < td class = "gutter" > < pre > < span class = "line" > 1< / span > < br > < span class = "line" > 2< / span > < br > < span class = "line" > 3< / span > < br > < span class = "line" > 4< / span > < br > < span class = "line" > 5< / span > < br > < span class = "line" > 6< / span > < br > < span class = "line" > 7< / span > < br > < span class = "line" > 8< / span > < br > < span class = "line" > 9< / span > < br > < span class = "line" > 10< / span > < br > < span class = "line" > 11< / span > < br > < span class = "line" > 12< / span > < br > < span class = "line" > 13< / span > < br > < span class = "line" > 14< / span > < br > < span class = "line" > 15< / span > < br > < span class = "line" > 16< / span > < br > < span class = "line" > 17< / span > < br > < span class = "line" > 18< / span > < br > < span class = "line" > 19< / span > < br > < / pre > < / td > < td class = "code" > < pre > < span class = "line" > < span class = "comment" > -- 存储过程< / span > < / span > < br > < span class = "line" > < span class = "comment" > -- 创建存储过程< / span > < / span > < br > < span class = "line" > < span class = "keyword" > create< / span > < span class = "keyword" > procedure< / span > p1()< / span > < br > < span class = "line" > < span class = "keyword" > begin< / span > < / span > < br > < span class = "line" > < span class = "keyword" > select< / span > < span class = "built_in" > count< / span > (< span class = "operator" > *< / span > ) < span class = "keyword" > from< / span > student;< / span > < br > < span class = "line" > < span class = "keyword" > end< / span > ;< / span > < br > < span class = "line" > < / span > < br > < span class = "line" > < span class = "comment" > -- 调用< / span > < / span > < br > < span class = "line" > < span class = "keyword" > call< / span > p1();< / span > < br > < span class = "line" > < / span > < br > < span class = "line" > < span class = "comment" > -- 查看< / span > < / span > < br > < span class = "line" > < span class = "comment" > -- 查询指定数据库的存储过程及状态信息< / span > < / span > < br > < span class = "line" > < span class = "comment" > -- 查询itcast数据库中定义的存储过程< / span > < / span > < br > < span class = "line" > < span class = "keyword" > select< / span > < span class = "operator" > *< / span > < span class = "keyword" > from< / span > information_schema.ROUTINES < span class = "keyword" > where< / span > ROUTINE_SCHEMA < span class = "operator" > =< / span > < span class = "string" > ' itcast' < / span > ;< / span > < br > < span class = "line" > < span class = "comment" > -- 查询某个存储过程的定义< / span > < / span > < br > < span class = "line" > < span class = "keyword" > SHOW< / span > < span class = "keyword" > CREATE< / span > < span class = "keyword" > PROCEDURE< / span > p1 ;< / span > < br > < span class = "line" > < / span > < br > < span class = "line" > < span class = "comment" > -- 删除< / span > < / span > < br > < span class = "line" > < span class = "keyword" > drop< / span > < span class = "keyword" > procedure< / span > if < span class = "keyword" > exists< / span > p1;< / span > < br > < / pre > < / td > < / tr > < / table > < / figure >
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< h4 id = "4-2-3-变量" > < a href = "#4-2-3-变量" class = "headerlink" title = "4.2.3 变量" > < / a > 4.2.3 变量< / h4 > < p > 在MySQL中变量分为三种类型: 系统变量、用户定义变量、局部变量< / p >
< h5 id = "4-2-3-1-系统变量" > < a href = "#4-2-3-1-系统变量" class = "headerlink" title = "4.2.3.1 系统变量" > < / a > 4.2.3.1 系统变量< / h5 > < p > 系统变量 是MySQL服务器提供， ， （ ） （ ） < / p >
< p > 1.查看系统变量< / p >
< figure class = "highlight sql" > < table > < tr > < td class = "gutter" > < pre > < span class = "line" > 1< / span > < br > < span class = "line" > 2< / span > < br > < span class = "line" > 3< / span > < br > < / pre > < / td > < td class = "code" > < pre > < span class = "line" > < span class = "keyword" > SHOW< / span > [ SESSION < span class = "operator" > |< / span > < span class = "keyword" > GLOBAL< / span > ] VARIABLES ; < span class = "comment" > -- 查看所有系统变量< / span > < / span > < br > < span class = "line" > < span class = "keyword" > SHOW< / span > [ SESSION < span class = "operator" > |< / span > < span class = "keyword" > GLOBAL< / span > ] VARIABLES < span class = "keyword" > LIKE< / span > < span class = "string" > ' ......' < / span > ; < span class = "comment" > -- 可以通过LIKE模糊匹配方式查找变量< / span > < / span > < br > < span class = "line" > < span class = "keyword" > SELECT< / span > @@[SESSION < span class = "operator" > |< / span > < span class = "keyword" > GLOBAL< / span > ] 系统变量名; < span class = "comment" > -- 查看指定变量的值< / span > < / span > < br > < / pre > < / td > < / tr > < / table > < / figure >
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< p > 2.设置系统变量< / p >
< figure class = "highlight sql" > < table > < tr > < td class = "gutter" > < pre > < span class = "line" > 1< / span > < br > < span class = "line" > 2< / span > < br > < / pre > < / td > < td class = "code" > < pre > < span class = "line" > < span class = "keyword" > SET< / span > [ SESSION < span class = "operator" > |< / span > < span class = "keyword" > GLOBAL< / span > ] 系统变量名 < span class = "operator" > =< / span > 值 ;< / span > < br > < span class = "line" > < span class = "keyword" > SET< / span > @@[SESSION < span class = "operator" > |< / span > < span class = "keyword" > GLOBAL< / span > ]系统变量名 < span class = "operator" > =< / span > 值 ;< / span > < br > < / pre > < / td > < / tr > < / table > < / figure >
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< blockquote >
< p > < strong > 注意< / strong > :< / p >
< pre > < code > 如果没有指定SESSION/GLOBAL， ，
< / code > < / pre >
< blockquote >
< p > 1 mysql服务重新启动之后， ， ， / etc/ my.cnf 中配置< / p >
< / blockquote >
< p > < / p >
< p > < / p >
< / blockquote >
< p > < strong > 演示示例< / strong > < / p >
< figure class = "highlight sql" > < table > < tr > < td class = "gutter" > < pre > < span class = "line" > 1< / span > < br > < span class = "line" > 2< / span > < br > < span class = "line" > 3< / span > < br > < span class = "line" > 4< / span > < br > < span class = "line" > 5< / span > < br > < span class = "line" > 6< / span > < br > < span class = "line" > 7< / span > < br > < span class = "line" > 8< / span > < br > < span class = "line" > 9< / span > < br > < span class = "line" > 10< / span > < br > < span class = "line" > 11< / span > < br > < span class = "line" > 12< / span > < br > < span class = "line" > 13< / span > < br > < span class = "line" > 14< / span > < br > < span class = "line" > 15< / span > < br > < span class = "line" > 16< / span > < br > < / pre > < / td > < td class = "code" > < pre > < span class = "line" > < span class = "comment" > -- 系统变量< / span > < / span > < br > < span class = "line" > < span class = "comment" > -- 查看所有系统变量< / span > < / span > < br > < span class = "line" > < span class = "keyword" > show< / span > session variables ; #查看会话的系统变量< / span > < br > < span class = "line" > < span class = "keyword" > show< / span > < span class = "keyword" > global< / span > variables ; #查看全局的系统变量< / span > < br > < span class = "line" > < span class = "comment" > -- 查看以auto开头的系统变量< / span > < / span > < br > < span class = "line" > < span class = "keyword" > show< / span > variables < span class = "keyword" > like< / span > < span class = "string" > ' auto%' < / span > ;< / span > < br > < span class = "line" > < span class = "comment" > -- 查看某一个具体的环境变量值（ ） < / span > < / span > < br > < span class = "line" > < span class = "keyword" > select< / span > @< span class = "variable" > @autocommit< / span > ; #会话的< / span > < br > < span class = "line" > < span class = "keyword" > select< / span > @< span class = "variable" > @global< / span > .autocommit; #全局的< / span > < br > < span class = "line" > < / span > < br > < span class = "line" > < span class = "comment" > -- 设置系统变量（ ） < / span > < / span > < br > < span class = "line" > < span class = "keyword" > set< / span > session autocommit < span class = "operator" > =< / span > < span class = "number" > 1< / span > ; #会话级别的< / span > < br > < span class = "line" > < span class = "keyword" > set< / span > < span class = "keyword" > global< / span > autocommit < span class = "operator" > =< / span > < span class = "number" > 1< / span > ; #全局级别的< / span > < br > < span class = "line" > < span class = "comment" > -- 或者< / span > < / span > < br > < span class = "line" > < span class = "keyword" > set< / span > @< span class = "variable" > @autocommit< / span > < span class = "operator" > =< / span > < span class = "number" > 1< / span > ;< / span > < br > < span class = "line" > < span class = "keyword" > set< / span > @< span class = "variable" > @global< / span > .autocommit < span class = "operator" > =< / span > < span class = "number" > 1< / span > ;< / span > < br > < / pre > < / td > < / tr > < / table > < / figure >
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< h5 id = "4-2-3-2-用户定义变量" > < a href = "#4-2-3-2-用户定义变量" class = "headerlink" title = "4.2.3.2 用户定义变量" > < / a > 4.2.3.2 用户定义变量< / h5 > < p > 用户定义变量 是用户根据需要自己定义的变量，用户变量不用提前声明，在用的时候直接用 “@变量 名” 使用就可以。其作用域为当前连接< / p >
< p > < strong > 1.赋值< / strong > < / p >
< p > 方式一：< / p >
< figure class = "highlight sql" > < table > < tr > < td class = "gutter" > < pre > < span class = "line" > 1< / span > < br > < span class = "line" > 2< / span > < br > < / pre > < / td > < td class = "code" > < pre > < span class = "line" > < span class = "keyword" > SET< / span > < span class = "variable" > @var_name< / span > < span class = "operator" > =< / span > expr [, < span class = "variable" > @var_name< / span > < span class = "operator" > =< / span > expr] ... ;< / span > < br > < span class = "line" > < span class = "keyword" > SET< / span > < span class = "variable" > @var_name< / span > :< span class = "operator" > =< / span > expr [, < span class = "variable" > @var_name< / span > :< span class = "operator" > =< / span > expr] ... ;< / span > < br > < / pre > < / td > < / tr > < / table > < / figure >
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< p > 赋值时，可以使用 = ，也可以使用 := < / p >
< p > 方式二:< / p >
< figure class = "highlight sql" > < table > < tr > < td class = "gutter" > < pre > < span class = "line" > 1< / span > < br > < span class = "line" > 2< / span > < br > < / pre > < / td > < td class = "code" > < pre > < span class = "line" > < span class = "keyword" > SELECT< / span > < span class = "variable" > @var_name< / span > :< span class = "operator" > =< / span > expr [, < span class = "variable" > @var_name< / span > :< span class = "operator" > =< / span > expr] ... ;< / span > < br > < span class = "line" > < span class = "keyword" > SELECT< / span > 字段名 < span class = "keyword" > INTO< / span > < span class = "variable" > @var_name< / span > < span class = "keyword" > FROM< / span > 表名;< / span > < br > < / pre > < / td > < / tr > < / table > < / figure >
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< p > < strong > 2.使用< / strong > < / p >
< figure class = "highlight sql" > < table > < tr > < td class = "gutter" > < pre > < span class = "line" > 1< / span > < br > < / pre > < / td > < td class = "code" > < pre > < span class = "line" > < span class = "keyword" > SELECT< / span > < span class = "variable" > @var_name< / span > ;< / span > < br > < / pre > < / td > < / tr > < / table > < / figure >
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< blockquote >
< p > 注意: 用户定义的变量无需对其进行声明或初始化， < / p >
< / blockquote >
< p > < strong > 演示示例< / strong > < / p >
< figure class = "highlight sql" > < table > < tr > < td class = "gutter" > < pre > < span class = "line" > 1< / span > < br > < span class = "line" > 2< / span > < br > < span class = "line" > 3< / span > < br > < span class = "line" > 4< / span > < br > < span class = "line" > 5< / span > < br > < span class = "line" > 6< / span > < br > < span class = "line" > 7< / span > < br > < span class = "line" > 8< / span > < br > < span class = "line" > 9< / span > < br > < span class = "line" > 10< / span > < br > < span class = "line" > 11< / span > < br > < span class = "line" > 12< / span > < br > < / pre > < / td > < td class = "code" > < pre > < span class = "line" > < span class = "comment" > -- 用户定义变量< / span > < / span > < br > < span class = "line" > < span class = "comment" > -- 赋值< / span > < / span > < br > < span class = "line" > < span class = "comment" > -- 方式一< / span > < / span > < br > < span class = "line" > < span class = "keyword" > set< / span > < span class = "variable" > @myname< / span > < span class = "operator" > =< / span > < span class = "string" > ' itcast' < / span > ;< / span > < br > < span class = "line" > < span class = "keyword" > set< / span > < span class = "variable" > @myage< / span > :< span class = "operator" > =< / span > < span class = "number" > 10< / span > ;< / span > < br > < span class = "line" > < span class = "keyword" > set< / span > < span class = "variable" > @mygender< / span > :< span class = "operator" > =< / span > < span class = "string" > ' 男' < / span > ,< span class = "variable" > @myhobby< / span > < span class = "operator" > =< / span > < span class = "string" > ' java' < / span > ;< / span > < br > < span class = "line" > < span class = "comment" > -- 方式二< / span > < / span > < br > < span class = "line" > < span class = "keyword" > select< / span > < span class = "variable" > @mycolor< / span > :< span class = "operator" > =< / span > < span class = "string" > ' red' < / span > ;< / span > < br > < span class = "line" > < span class = "keyword" > select< / span > < span class = "built_in" > count< / span > (< span class = "operator" > *< / span > ) < span class = "keyword" > into< / span > < span class = "variable" > @mycount< / span > < span class = "keyword" > from< / span > tb_user; #将tb_user表中的总记录数赋值给< span class = "variable" > @mycount< / span > < / span > < br > < span class = "line" > < / span > < br > < span class = "line" > < span class = "comment" > -- 使用< / span > < / span > < br > < span class = "line" > < span class = "keyword" > select< / span > < span class = "variable" > @myname< / span > ,< span class = "variable" > @myage< / span > ,< span class = "variable" > @mygender< / span > ,< span class = "variable" > @myhobby< / span > ,< span class = "variable" > @mycolor< / span > ,< span class = "variable" > @mycount< / span > ;< / span > < br > < / pre > < / td > < / tr > < / table > < / figure >
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< h5 id = "4-2-3-3-局部变量" > < a href = "#4-2-3-3-局部变量" class = "headerlink" title = "4.2.3.3 局部变量" > < / a > 4.2.3.3 局部变量< / h5 > < p > 局部变量 是根据需要定义的在局部生效的变量， ， ， < / p >
< p > 1**.声明**< / p >
< figure class = "highlight sql" > < table > < tr > < td class = "gutter" > < pre > < span class = "line" > 1< / span > < br > < / pre > < / td > < td class = "code" > < pre > < span class = "line" > < span class = "keyword" > DECLARE< / span > 变量名 变量类型 [< span class = "keyword" > DEFAULT< / span > ... ] ;< / span > < br > < / pre > < / td > < / tr > < / table > < / figure >
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< p > 变量类型就是数据库字段类型： < / p >
< p > < strong > 2.赋值< / strong > < / p >
< figure class = "highlight sql" > < table > < tr > < td class = "gutter" > < pre > < span class = "line" > 1< / span > < br > < span class = "line" > 2< / span > < br > < span class = "line" > 3< / span > < br > < / pre > < / td > < td class = "code" > < pre > < span class = "line" > < span class = "keyword" > SET< / span > 变量名 < span class = "operator" > =< / span > 值 ;< / span > < br > < span class = "line" > < span class = "keyword" > SET< / span > 变量名 :< span class = "operator" > =< / span > 值 ;< / span > < br > < span class = "line" > < span class = "keyword" > SELECT< / span > 字段名 < span class = "keyword" > INTO< / span > 变量名 < span class = "keyword" > FROM< / span > 表名 ... ;< / span > < br > < / pre > < / td > < / tr > < / table > < / figure >
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< p > < strong > 演示示例< / strong > < / p >
< figure class = "highlight sql" > < table > < tr > < td class = "gutter" > < pre > < span class = "line" > 1< / span > < br > < span class = "line" > 2< / span > < br > < span class = "line" > 3< / span > < br > < span class = "line" > 4< / span > < br > < span class = "line" > 5< / span > < br > < span class = "line" > 6< / span > < br > < span class = "line" > 7< / span > < br > < span class = "line" > 8< / span > < br > < span class = "line" > 9< / span > < br > < span class = "line" > 10< / span > < br > < span class = "line" > 11< / span > < br > < span class = "line" > 12< / span > < br > < span class = "line" > 13< / span > < br > < span class = "line" > 14< / span > < br > < / pre > < / td > < td class = "code" > < pre > < span class = "line" > < span class = "comment" > -- 局部变量< / span > < / span > < br > < span class = "line" > < span class = "comment" > -- 创建存储过程< / span > < / span > < br > < span class = "line" > < span class = "keyword" > create< / span > < span class = "keyword" > procedure< / span > p2()< / span > < br > < span class = "line" > < span class = "keyword" > begin< / span > < / span > < br > < span class = "line" > # 定义一个< span class = "type" > int< / span > 类型的局部变量,默认值是< span class = "number" > 0< / span > < / span > < br > < span class = "line" > < span class = "keyword" > declare< / span > stu_count < span class = "type" > int< / span > < span class = "keyword" > default< / span > < span class = "number" > 0< / span > ;< / span > < br > < span class = "line" > # 给stu_count赋值< / span > < br > < span class = "line" > < span class = "comment" > -- set stu_count = 100;< / span > < / span > < br > < span class = "line" > < span class = "keyword" > select< / span > < span class = "built_in" > count< / span > (< span class = "operator" > *< / span > ) < span class = "keyword" > into< / span > stu_count < span class = "keyword" > from< / span > tb_user;< / span > < br > < span class = "line" > #输出< / span > < br > < span class = "line" > < span class = "keyword" > select< / span > stu_count;< / span > < br > < span class = "line" > < span class = "keyword" > end< / span > ;< / span > < br > < span class = "line" > < span class = "comment" > -- 调用函数< / span > < / span > < br > < span class = "line" > < span class = "keyword" > call< / span > p2();< / span > < br > < / pre > < / td > < / tr > < / table > < / figure >
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< h4 id = "4-2-4-if判断" > < a href = "#4-2-4-if判断" class = "headerlink" title = "4.2.4 if判断" > < / a > 4.2.4 if判断< / h4 > < p > < strong > 介绍< / strong > < / p >
< p > if 用于做条件判断，具体的语法结构为：< / p >
< figure class = "highlight sql" > < table > < tr > < td class = "gutter" > < pre > < span class = "line" > 1< / span > < br > < span class = "line" > 2< / span > < br > < span class = "line" > 3< / span > < br > < span class = "line" > 4< / span > < br > < span class = "line" > 5< / span > < br > < span class = "line" > 6< / span > < br > < span class = "line" > 7< / span > < br > < / pre > < / td > < td class = "code" > < pre > < span class = "line" > IF 条件< span class = "number" > 1< / span > < span class = "keyword" > THEN< / span > < / span > < br > < span class = "line" > .....< / span > < br > < span class = "line" > ELSEIF 条件< span class = "number" > 2< / span > < span class = "keyword" > THEN< / span > < span class = "comment" > -- 可选< / span > < / span > < br > < span class = "line" > .....< / span > < br > < span class = "line" > < span class = "keyword" > ELSE< / span > < span class = "comment" > -- 可选< / span > < / span > < br > < span class = "line" > .....< / span > < br > < span class = "line" > < span class = "keyword" > END< / span > IF;< / span > < br > < / pre > < / td > < / tr > < / table > < / figure >
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< p > 在if条件判断的结构中， ， < / p >
< p > < strong > 案例< / strong > < / p >
< p > 根据定义的分数score变量， < / p >
< ul >
< li > < p > score > = 85分， < / p >
< / li >
< li > < p > score > = 60分 且 score < 85分， < / p >
< / li >
< li > < p > score < 60分， < / p >
< / li >
< / ul >
< figure class = "highlight sql" > < table > < tr > < td class = "gutter" > < pre > < span class = "line" > 1< / span > < br > < span class = "line" > 2< / span > < br > < span class = "line" > 3< / span > < br > < span class = "line" > 4< / span > < br > < span class = "line" > 5< / span > < br > < span class = "line" > 6< / span > < br > < span class = "line" > 7< / span > < br > < span class = "line" > 8< / span > < br > < span class = "line" > 9< / span > < br > < span class = "line" > 10< / span > < br > < span class = "line" > 11< / span > < br > < span class = "line" > 12< / span > < br > < span class = "line" > 13< / span > < br > < span class = "line" > 14< / span > < br > < span class = "line" > 15< / span > < br > < span class = "line" > 16< / span > < br > < span class = "line" > 17< / span > < br > < span class = "line" > 18< / span > < br > < span class = "line" > 19< / span > < br > < span class = "line" > 20< / span > < br > < span class = "line" > 21< / span > < br > < span class = "line" > 22< / span > < br > < span class = "line" > 23< / span > < br > < / pre > < / td > < td class = "code" > < pre > < span class = "line" > < span class = "comment" > -- if判断< / span > < / span > < br > < span class = "line" > < span class = "comment" > -- 根据定义的分数score变量， < / span > < / span > < br > < span class = "line" > < span class = "comment" > -- score > = 85分， < / span > < / span > < br > < span class = "line" > < span class = "comment" > -- score > = 60分 且 score < 85分， < / span > < / span > < br > < span class = "line" > < span class = "comment" > -- score < 60分， < / span > < / span > < br > < span class = "line" > < span class = "keyword" > drop< / span > < span class = "keyword" > procedure< / span > p3;< / span > < br > < span class = "line" > < span class = "keyword" > create< / span > < span class = "keyword" > procedure< / span > p3()< / span > < br > < span class = "line" > < span class = "keyword" > begin< / span > < / span > < br > < span class = "line" > # 先给一个默认值 < span class = "number" > 58< / span > < / span > < br > < span class = "line" > < span class = "keyword" > declare< / span > score < span class = "type" > int< / span > < span class = "keyword" > default< / span > < span class = "number" > 58< / span > ;< / span > < br > < span class = "line" > < span class = "keyword" > declare< / span > < span class = "keyword" > result< / span > < span class = "type" > varchar< / span > (< span class = "number" > 10< / span > );< / span > < br > < span class = "line" > if score < span class = "operator" > > =< / span > < span class = "number" > 85< / span > < span class = "keyword" > then< / span > < / span > < br > < span class = "line" > < span class = "keyword" > set< / span > < span class = "keyword" > result< / span > :< span class = "operator" > =< / span > < span class = "string" > ' 优秀' < / span > ;< / span > < br > < span class = "line" > elseif score < span class = "operator" > > =< / span > < span class = "number" > 60< / span > < span class = "keyword" > then< / span > < / span > < br > < span class = "line" > < span class = "keyword" > set< / span > < span class = "keyword" > result< / span > :< span class = "operator" > =< / span > < span class = "string" > ' 及格' < / span > ;< / span > < br > < span class = "line" > < span class = "keyword" > else< / span > < / span > < br > < span class = "line" > < span class = "keyword" > set< / span > < span class = "keyword" > result< / span > :< span class = "operator" > =< / span > < span class = "string" > ' 不及格' < / span > ;< / span > < br > < span class = "line" > < span class = "keyword" > end< / span > if;< / span > < br > < span class = "line" > #输出< / span > < br > < span class = "line" > < span class = "keyword" > select< / span > < span class = "keyword" > result< / span > ;< / span > < br > < span class = "line" > < span class = "keyword" > end< / span > ;< / span > < br > < span class = "line" > < span class = "comment" > -- 调用< / span > < / span > < br > < span class = "line" > < span class = "keyword" > call< / span > p3();< / span > < br > < / pre > < / td > < / tr > < / table > < / figure >
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< h4 id = "4-2-5-参数" > < a href = "#4-2-5-参数" class = "headerlink" title = "4.2.5 参数" > < / a > 4.2.5 参数< / h4 > < p > < strong > 介绍< / strong > < / p >
< p > 参数的类型， ： < / p >
< p > < img src = "/pictures/image-20231006213944694.png" alt = "image-20231006213944694" > < / p >
< p > 语法< / p >
< figure class = "highlight sql" > < table > < tr > < td class = "gutter" > < pre > < span class = "line" > 1< / span > < br > < span class = "line" > 2< / span > < br > < span class = "line" > 3< / span > < br > < span class = "line" > 4< / span > < br > < / pre > < / td > < td class = "code" > < pre > < span class = "line" > < span class = "keyword" > CREATE< / span > < span class = "keyword" > PROCEDURE< / span > 存储过程名称 ([ < span class = "keyword" > IN< / span > < span class = "operator" > /< / span > < span class = "keyword" > OUT< / span > < span class = "operator" > /< / span > < span class = "keyword" > INOUT< / span > 参数名 参数类型 ])< / span > < br > < span class = "line" > < span class = "keyword" > BEGIN< / span > < / span > < br > < span class = "line" > < span class = "comment" > -- SQL语句< / span > < / span > < br > < span class = "line" > < span class = "keyword" > END< / span > ;< / span > < br > < / pre > < / td > < / tr > < / table > < / figure >
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< p > < strong > 案例< / strong > < / p >
< p > 1.根据传入的分数score变量， ， < / p >
< ul >
< li > < p > score > = 85分， < / p >
< / li >
< li > < p > score > = 60分 且 score < 85分， < / p >
< / li >
< li > < p > score < 60分， < / p >
< / li >
< / ul >
< figure class = "highlight sql" > < table > < tr > < td class = "gutter" > < pre > < span class = "line" > 1< / span > < br > < span class = "line" > 2< / span > < br > < span class = "line" > 3< / span > < br > < span class = "line" > 4< / span > < br > < span class = "line" > 5< / span > < br > < span class = "line" > 6< / span > < br > < span class = "line" > 7< / span > < br > < span class = "line" > 8< / span > < br > < span class = "line" > 9< / span > < br > < span class = "line" > 10< / span > < br > < span class = "line" > 11< / span > < br > < span class = "line" > 12< / span > < br > < span class = "line" > 13< / span > < br > < span class = "line" > 14< / span > < br > < span class = "line" > 15< / span > < br > < span class = "line" > 16< / span > < br > < span class = "line" > 17< / span > < br > < span class = "line" > 18< / span > < br > < span class = "line" > 19< / span > < br > < / pre > < / td > < td class = "code" > < pre > < span class = "line" > < span class = "comment" > -- 参数< / span > < / span > < br > < span class = "line" > < span class = "comment" > -- 1.根据传入的分数score变量， ， < / span > < / span > < br > < span class = "line" > < span class = "comment" > -- score > = 85分， < / span > < / span > < br > < span class = "line" > < span class = "comment" > -- score > = 60分 且 score < 85分， < / span > < / span > < br > < span class = "line" > < span class = "comment" > -- score < 60分， < / span > < / span > < br > < span class = "line" > < span class = "keyword" > create< / span > < span class = "keyword" > procedure< / span > p4(< span class = "keyword" > in< / span > score < span class = "type" > int< / span > , < span class = "keyword" > out< / span > < span class = "keyword" > result< / span > < span class = "type" > varchar< / span > (< span class = "number" > 10< / span > ))< / span > < br > < span class = "line" > < span class = "keyword" > begin< / span > < / span > < br > < span class = "line" > if score < span class = "operator" > > =< / span > < span class = "number" > 85< / span > < span class = "keyword" > then< / span > < / span > < br > < span class = "line" > < span class = "keyword" > set< / span > < span class = "keyword" > result< / span > :< span class = "operator" > =< / span > < span class = "string" > ' 优秀' < / span > ;< / span > < br > < span class = "line" > elseif score < span class = "operator" > > =< / span > < span class = "number" > 60< / span > < span class = "keyword" > then< / span > < / span > < br > < span class = "line" > < span class = "keyword" > set< / span > < span class = "keyword" > result< / span > :< span class = "operator" > =< / span > < span class = "string" > ' 及格' < / span > ;< / span > < br > < span class = "line" > < span class = "keyword" > else< / span > < / span > < br > < span class = "line" > < span class = "keyword" > set< / span > < span class = "keyword" > result< / span > :< span class = "operator" > =< / span > < span class = "string" > ' 不及格' < / span > ;< / span > < br > < span class = "line" > < span class = "keyword" > end< / span > if;< / span > < br > < span class = "line" > < span class = "keyword" > end< / span > ;< / span > < br > < span class = "line" > < span class = "comment" > -- 调用< / span > < / span > < br > < span class = "line" > < span class = "keyword" > call< / span > p4(< span class = "number" > 88< / span > ,< span class = "variable" > @result< / span > );< / span > < br > < span class = "line" > < span class = "comment" > -- 查看结果< / span > < / span > < br > < span class = "line" > < span class = "keyword" > select< / span > < span class = "variable" > @result< / span > ;< / span > < br > < / pre > < / td > < / tr > < / table > < / figure >
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< p > 2.将传入的200分制的分数， ， ， < / p >
< figure class = "highlight sql" > < table > < tr > < td class = "gutter" > < pre > < span class = "line" > 1< / span > < br > < span class = "line" > 2< / span > < br > < span class = "line" > 3< / span > < br > < span class = "line" > 4< / span > < br > < span class = "line" > 5< / span > < br > < span class = "line" > 6< / span > < br > < span class = "line" > 7< / span > < br > < span class = "line" > 8< / span > < br > < span class = "line" > 9< / span > < br > < / pre > < / td > < td class = "code" > < pre > < span class = "line" > < span class = "comment" > -- 2.将传入的200分制的分数， ， ， < / span > < / span > < br > < span class = "line" > < span class = "keyword" > create< / span > < span class = "keyword" > procedure< / span > p5(< span class = "keyword" > inout< / span > score < span class = "keyword" > double< / span > )< / span > < br > < span class = "line" > < span class = "keyword" > begin< / span > < / span > < br > < span class = "line" > < span class = "keyword" > set< / span > score :< span class = "operator" > =< / span > score < span class = "operator" > *< / span > < span class = "number" > 0.5< / span > ;< / span > < br > < span class = "line" > < span class = "keyword" > end< / span > ;< / span > < br > < span class = "line" > < span class = "comment" > -- 调用(score既是输入又是输出)< / span > < / span > < br > < span class = "line" > < span class = "keyword" > set< / span > < span class = "variable" > @score< / span > < span class = "operator" > =< / span > < span class = "number" > 78< / span > ;< / span > < br > < span class = "line" > < span class = "keyword" > call< / span > p5(< span class = "variable" > @score< / span > );< / span > < br > < span class = "line" > < span class = "keyword" > select< / span > < span class = "variable" > @score< / span > ;< / span > < br > < / pre > < / td > < / tr > < / table > < / figure >
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< h4 id = "4-2-6-case" > < a href = "#4-2-6-case" class = "headerlink" title = "4.2.6 case" > < / a > 4.2.6 case< / h4 > < / article > < div class = "tag_share" > < div class = "post-meta__tag-list" > < a class = "post-meta__tags" href = "/tags/Mysql/" > Mysql< / a > < / div > < div class = "post_share" > < div class = "social-share" data-image = "/img/9.png" data-sites = "wechat,weibo,qq" > < / div > < link rel = "stylesheet" href = "/cdn/css/share.min.css" media = "print" onload = "this.media='all'" > < script src = "/cdn/js/social-share.min.js" defer > < / script > < / div > < / div > < div class = "post-reward" > < div class = "reward-button" > < i class = "fas fa-qrcode" > < / i > 打赏< / div > < div class = "reward-main" > < ul class = "reward-all" > < li class = "reward-item" > < a href = "/img/wechat.jpg" target = "_blank" > < img class = "post-qr-code-img" src = "/img/wechat.jpg" alt = "微信" / > < / a > < div class = "post-qr-code-desc" > 微信< / div > < / li > < li class = "reward-item" > < a href = "/img/alipay.jpg" target = "_blank" > < img class = "post-qr-code-img" src = "/img/alipay.jpg" alt = "支付宝" / > < / a > < div class = "post-qr-code-desc" > 支付宝< / div > < / li > < / ul > < / div > < / div > < br / > < div id = "post-comment" > < div class = "comment-head" > < div class = "comment-headline" > < i class = "far fa-comment-alt fa-fw" > < / i > < span > 评论< / span > < / div > < / div > < div class = "comment-wrap" > < div > < div id = "gitalk-container" > < / div > < / div > < / div > < / div > < / div > < div class = "aside-content" id = "aside-content" > < div class = "card-widget card-info" > < div class = "is-center" > < div class = "avatar-img" > < img src = "/img/avatar.jpg" onerror = "this.onerror=null;this.src='/img/loading.gif'" alt = "avatar" / > < / div > < div class = "author-info__name" > Jason< / div > < div class = "author-info__description" > Debug the World！ < / div > < / div > < div class = "card-info-data site-data is-center" > < a href = "/archives/" > < div class = "headline" > 文章< / div > < div class = "length-num" > 60< / div > < / a > < a href = "/tags/" > < div class = "headline" > 标签< / div > < div class = "length-num" > 39< / div > < / a > < a href = "/categories/" > < div class = "headline" > 分类< / div > < div class = "length-num" > 10< / div > < / a > < / div > < a id = "card-info-btn" > < i class = "fab fa-microsoft" > < / i > < span > Ctrl + D 收藏< / span > < / a > < div class = "card-info-social-icons is-center" > < a class = "social-icon" href = "https://github.com/JasonsGong" target = "_blank" title = "Github" > < i class = "fab fa-github" > < / i > < / a > < a class = "social-icon" href = "tencent://AddContact/?fromId=45&fromSubId=1&subcmd=all&uin=2602183349&website=www.oicqzone.com" target = "_blank" title = "QQ" > < i class = "fab fa-qq" > < / i > < / a > < a class = "social-icon" href = "mailto:2602183349@qq.com" target = "_blank" title = "Email" > < i class = "fas fa-envelope-open-text" > < / i > < / a > < a class = "social-icon" href = "https://github.com/JasonsGong?tab=repositories" target = "_blank" title = "代码仓库" > < i class = "fas fa-database" > < / i > < / a > < / div > < / div > < div class = "card-widget card-announcement" > < div class = "item-headline" > < i class = "fas fa-bullhorn fa-shake" > < / i > < span > 公告< / span > < / div > < div class = "announcement_content" > 本网站是静态网站,更新页面资源请使用Ctrl+F5;若网站内文章对你有帮助,请使用Ctrl+D收藏该网站！ < / div > < / div > < div class = "sticky_layout" > < div class = "card-widget" id = "card-toc" > < div class = "item-headline" > < i class = "fas fa-stream" > < / i > < span > 目录< / span > < span class = "toc-percentage" > < / span > < / div > < div class = "toc-content is-expand" > < ol class = "toc" > < li class = "toc-item toc-level-1" > < a class = "toc-link" href = "#%E4%B8%80-Mysql%E5%85%A5%E9%97%A8" > < span class = "toc-text" > 一.Mysql入门< / span > < / a > < ol class = "toc-child" > < li class = "toc-item toc-level-2" > < a class = "toc-link" href = "#1-SQL" > < span class = "toc-text" > 1.SQL< / span > < / a > < ol class = "toc-child" > < li class = "toc-item toc-level-3" > < a class = "toc-link" href = "#1-1-SQL%E9%80%9A%E7%94%A8%E8%AF%AD%E6%B3%95" > < span class = "toc-text" > 1.1 SQL通用语法< / span > < / a > < / li > < li class = "toc-item toc-level-3" > < a class = "toc-link" href = "#1-2-SQL%E5%88%86%E7%B1%BB" > < span class = "toc-text" > 1.2 SQL分类< / span > < / a > < / li > < li class = "toc-item toc-level-3" > < a class = "toc-link" href = "#1-3-DDL-%E6%95%B0%E6%8D%AE%E5%AE%9A%E4%B9%89%E8%AF%AD%E8%A8%80" > < span class = "toc-text" > 1.3 DDL-数据定义语言< / span > < / a > < / li > < li class = "toc-item toc-level-3" > < a class = "toc-link" href = "#1-4-DML-%E6%95%B0%E6%8D
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var item_html = '< div class = "recent-post-item" style = "height: auto;width: 100%" > < div class = "blog-slider swiper-container-fade swiper-container-horizontal" id = "swiper_container" > < div class = "blog-slider__wrp swiper-wrapper" style = "transition-duration: 0ms;" > < div class = "blog-slider__item swiper-slide" style = "width: 750px; opacity: 1; transform: translate3d(0px, 0px, 0px); transition-duration: 0ms;" > < a class = "blog-slider__img" href = "posts/19306.html" alt = "" > < img width = "48" height = "48" src = "/img/1.png" alt = "" onerror = "this.src=https://unpkg.zhimg.com/akilar-candyassets/image/loading.gif; this.onerror = null;" / > < / a > < div class = "blog-slider__content" > < span class = "blog-slider__code" > 2023-04-21< / span > < a class = "blog-slider__title" href = "posts/19306.html" alt = "" > Docker容器化技术< / a > < div class = "blog-slider__text" > Docker< / div > < a class = "blog-slider__button" href = "posts/19306.html" alt = "" > 详情 < / a > < / div > < / div > < div class = "blog-slider__item swiper-slide" style = "width: 750px; opacity: 1; transform: translate3d(0px, 0px, 0px); transition-duration: 0ms;" > < a class = "blog-slider__img" href = "posts/47003.html" alt = "" > < img width = "48" height = "48" src = "/img/5.png" alt = "" onerror = "this.src=https://unpkg.zhimg.com/akilar-candyassets/image/loading.gif; this.onerror = null;" / > < / a > < div class = "blog-slider__content" > < span class = "blog-slider__code" > 2023-03-10< / span > < a class = "blog-slider__title" href = "posts/47003.html" alt = "" > 常用正则表达式大全< / a > < div class = "blog-slider__text" > 正则表达式< / div > < a class = "blog-slider__button" href = "posts/47003.html" alt = "" > 详情 < / a > < / div > < / div > < div class = "blog-slider__item swiper-slide" style = "width: 750px; opacity: 1; transform: translate3d(0px, 0px, 0px); transition-duration: 0ms;" > < a class = "blog-slider__img" href = "posts/20683.html" alt = "" > < img width = "48" height = "48" src = "/img/8.png" alt = "" onerror = "this.src=https://unpkg.zhimg.com/akilar-candyassets/image/loading.gif; this.onerror = null;" / > < / a > < div class = "blog-slider__content" > < span class = "blog-slider__code" > 2023-06-05< / span > < a class = "blog-slider__title" href = "posts/20683.html" alt = "" > Linux中开发环境的搭建< / a > < div class = "blog-slider__text" > 环境搭建< / div > < a class = "blog-slider__button" href = "posts/20683.html" alt = "" > 详情 < / a > < / div > < / div > < div class = "blog-slider__item swiper-slide" style = "width: 750px; opacity: 1; transform: translate3d(0px, 0px, 0px); transition-duration: 0ms;" > < a class = "blog-slider__img" href = "posts/63333.html" alt = "" > < img width = "48" height = "48" src = "/img/10.png" alt = "" onerror = "this.src=https://unpkg.zhimg.com/akilar-candyassets/image/loading.gif; this.onerror = null;" / > < / a > < div class = "blog-slider__content" > < span class = "blog-slider__code" > 2023-06-03< / span > < a class = "blog-slider__title" href = "posts/63333.html" alt = "" > 开发环境的搭建< / a > < div class = "blog-slider__text" > 环境搭建< / div > < a class = "blog-slider__button" href = "posts/63333.html" alt = "" > 详情 < / a > < / div > < / div > < / div > < div class = "blog-slider__pagination swiper-pagination-clickable swiper-pagination-bullets" > < / div > < / div > < / div > ';
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