2137 lines
73 KiB
Markdown
2137 lines
73 KiB
Markdown
# MySQL
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## 数据库概念
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数据(data)是事实或观察的结果，是对客观事物的逻辑归纳，是用于表示客观事物的未经加工的的原始素材。
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数据可以是连续的值，比如声音、图像，称为模拟数据。也可以是离散的，如符号、文字，称为数字数据。
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在计算机系统中，数据以二进制信息单元0,1的形式表示。
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**数据的定义:**数据是指对客观事件进行记录并可以鉴别的符号，是对客观事物的性质、状态以及相互关系等进行记载的物理符号或这些物理符号的组合。它是可识别的、抽象的符号。
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DBMS（database management system）
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### DBMS类别
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#### RDBMS
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以多张二维表的方式来存储，又给多张表建立了一定的关系（关系型数据库）
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#### NoSQL
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nosql 很多以json格式进行存储数据的（mogodb）
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#### DBMS对比
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##### 功能对比
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| | 关系型数据库 | 非关系型数据库 |
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| --- | --- | --- |
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| 强大的查询功能 | √ | × |
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| 强一致性 | √ | × |
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| 二级索引 | √ | × |
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| 灵活模式 | × | √ |
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| 扩展性 | × | √ |
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| 性能 | × | √ |
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##### 特点对比
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- 关系型数据库（RDBMS）的特点：
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- 二维表
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- 典型产品Oracle传统企业，MySQL互联网企业
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- 数据存取是通过SQL（Structured Query Language结构化查询语言）
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- 最大特点数据安全性方面强（ACID）
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- 非关系型数据库（NoSQL：Not only SQL）的特点：
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- 不是否定关系型数据库，而是做关系型数据库的补充
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## MySQL基础操作
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在mysql官方网站可以下载到mysql的各种版本：[https://downloads.mysql.com/archives/installer/](https://downloads.mysql.com/archives/installer/)
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### 用户管理
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用户的定义
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- username@'主机域'
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- 主机域:可以理解为是Mysql登录的白名单
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- 主机域格式：
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- 10.1.1.12
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- 10.1.0.1%
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- 10.1.0.%
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- 10.1.%.%
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- %
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- localhost
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- 192.168.1.1/255.255.255.
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- 创建用户
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```sql
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mysql> create user user01@'192.168.175.%' identified by '123456';
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```
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- 查看用户
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```sql
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mysql> select user,host from mysql.user;
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```
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- 删除用户
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```sql
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mysql> drop user user01@'192.168.175.%';
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```
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- 修改密码
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```sql
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mysql> set password=PASSOWRD('123456')
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mysql> update user set password=PASSWORD('user01') where user='root' and host='localhost';
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mysql> grant all privileges on *.* to user01@'192.168.175.%' identified by '123456';
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mysql> flush privileges;
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```
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### 用户权限介绍
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- 权限
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```sql
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INSERT,SELECT, UPDATE, DELETE, CREATE, DROP, RELOAD, SHUTDOWN, PROCESS, FILE, REFERENCES, INDEX, ALTER, SHOW DATABASES, SUPER, CREATE TEMPORARY TABLES, LOCK TABLES, EXECUTE, REPLICATION SLAVE, REPLICATION CLIENT, CREATE VIEW, SHOW VIEW, CREATE ROUTINE, ALTER ROUTINE, CREATE USER, EVENT, TRIGGER, CREATE TABLESPACE
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```
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- 每次设定只能有一个属主，没有属组或其他用户的概念
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```sql
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grant all privileges on *.* to user01@''192.168.175.%'' identified by ''123'';
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权限 作用对象 归属 密码
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```
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作用对象分解
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- `_*.*_`[当前MySQL实例中所有库下的所有表]
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- wordpress.* [当前MySQL实例中wordpress库中所有表（单库级别）]
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- wordpress.user [当前MySQL实例中wordpress库中的user表（单表级别）]
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企业中权限的设定
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- 开发人员说：给我开一个用户
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- 沟通
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- 你需要对哪些库、表进行操作
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- 你从哪里连接过来
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- 用户名有没有要求
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- 密码要求
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- 发邮件
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- 一般给开发创建用户权限
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```sql
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grant select,update,delete,insert on *.* to 'user01@192.168.175.%' identified by '123456';
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```
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实验思考问题
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```sql
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##创建wordpress数据库
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create database wordpress;
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##使用wordpress库
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use wordpress;
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##创建t1、t2表
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create table t1 (id int);
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create table t2 (id int);
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##创建blog库
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create database blog;
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##使用blog库
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use blog;
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##创建t1表
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create table tb1 (id int);
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```
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授权
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```sql
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1、grant select on *.* to wordpress@’10.0.0.5%’ identified by ‘123’;
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2、grant insert,delete,update on wordpress.* to wordpress@’10.0.0.5%’ identified by ‘123’;
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3、grant all on wordpress.t1 to wordpress@’10.0.0.5%’ identified by ‘123’;
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```
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- 一个客户端程序使用wordpress用户登陆到10.0.0.51的MySQL后，
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- 对t1表的管理能力？
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- 对t2表的管理能力？
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- 对tb1表的管理能力？
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- 解
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- 同时满足1，2，3，最终权限是1+2+3
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- 同时满足了1和2两个授权，最终权限是1+2
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- 只满足1授权，所以只能select
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- 结论
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- 如果在不同级别都包含某个表的管理能力时，权限是相加关系。
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- 但是我们不推荐在多级别定义重复权限。
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- 最常用的权限设定方式是单库级别授权，即：wordpress.*
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## SQL语句
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- SQL是结构化的查询语句
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- SQL的种类
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- DDL:数据定义语句
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- DCL:数据控制语言
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- DML:数据操作语言
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- DQL:数据查询语言
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### DDL数据定义语句
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- 对库或者表进行操作的语句
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- 创建数据库
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```sql
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create database db01;
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## 创建数据库
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create database DB01;
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## 数据库名区分大小写(注意windows里面不区分)
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show databases;
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## 查看数据库(DQL)
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show create database db01;
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## 查看创建数据库语句
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help create database;
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## 查看创建数据库语句帮助
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create database db02 charset utf8;
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## 创建数据库的时候添加属性
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```
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- 删除数据库
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```sql
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drop database db02;
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## 删除数据库db02
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```
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- 修改定义库
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```sql
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alter database db01 charset utf8;
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show create database db01;
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```
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- 创建表
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```sql
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help create table;
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## 查看创表语句的帮助
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create table student(
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sid int,
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sname varchar(20),
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sage tinyint,
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sgender enum('m','f'),
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comtime datetime
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);
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## 创建表，并且定义每一列
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```
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- 数据类型(下面有完整的)
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| int | 整数 -231~230 |
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| --- | --- |
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| tinyint | 整数 -128~127 |
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| varchar | 字符类型(可变长) |
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| char | 字符类型(定长) |
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| enum | 枚举类型 |
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| datetime | 时间类型 年月日时分秒 |
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```sql
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create table student(
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sid int not null primary key auto_increment comment '学号',
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sname varchar(20) not null comment '学生姓名',
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sgender enum('m','f') not null default 'm' comment '学生性别',
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cometime datetime not null comment '入学时间'
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)charset utf8 engine innodb;
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## 带数据属性创建学生表
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show create table student;
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## 查看建表语句
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show tables;
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## 查看表
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desc student;
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## 查看表中列的定义信息
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```
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- 数据属性
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| not null | 不允许是空 |
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| --- | --- |
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| primary key | 主键(唯一且非空) |
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| auto_increment | 自增，此列必须是primary key或者unique key |
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| unique key | 单独的唯一的 |
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| default | 默认值 |
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| unsigned | 非负数 |
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| comment | 注释 |
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- 删除表
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```sql
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drop table student;
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```
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- 修改表的定义
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```sql
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alter table student rename stu;
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## 修改表名
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alter table stu add age int;
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## 添加列和列数据类型的定义
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alter table stu add test varchar(20),add qq int;
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## 添加多个列
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alter table stu add classid varchar(20) first;
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## 指定位置进行添加列(表首)
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alter table stu add phone int after age;
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## 指定位置进行添加列（指定列）
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alter table stu drop qq;
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## 删除指定的列及定义
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alter table stu modify sid varchar(20);
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## 修改列及定义（列属性）
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alter table stu change phone telphone char(20);
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## 修改列及定义（列名及属性）
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```
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#### 多表结构的创建与分析
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**如何找出两张表之间的关系**
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分析步骤： 1. 先站在左表的角度去找 是否左表的多条记录可以对应右表的一条记录，如果是，则证明左表的一个字段foreign key 右表一个字段（通常是id） **2. **再站在右表的角度去找 是否右表的多条记录可以对应左表的一条记录，如果是，则证明右表的一个字段foreign key 左表一个字段（通常是id） **3. **总结： **多对一** 如果只有步骤1成立，则是左表多对一右表 如果只有步骤2成立，则是右表多对一左表 **多对多 **
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如果步骤1和2同时成立，则证明这两张表时一个双向的多对一，即多对多,需要定义一个这两张表的关系表来专门存放二者的关系
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**一对一**
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如果1和2都不成立，而是左表的一条记录唯一对应右表的一条记录，反之亦然。这种情况很简单，就是在左表foreign key右表的基础上，将左表的外键字段设置成unique即可
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#### 建立表之间的关系
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**一对多或称为多对一**
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创建三张表：出版社，作者信息，书籍列表
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一对多（或多对一）：一个出版社可以出版多本书
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```sql
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create table press(
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id int primary key auto_increment,
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name varchar(20)
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);
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create table book(
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id int primary key auto_increment,
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name varchar(20),
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press_id int not null,
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foreign key(press_id) references press(id)
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on delete cascade
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on update cascade
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);
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insert into press(name) values
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('英格科技出版社'),
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('许老师YYDS出版社'),
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('安全渗透出版社')
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;
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insert into book(name,press_id) values
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('九阳神功',1),
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('九阴真经',2),
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('九阴白骨爪',2),
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('独孤九剑',3),
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('降龙十巴掌',2),
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('葵花宝典',3)
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;
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```
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**多对多**
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三张表：出版社，作者信息，书
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多对多：一个作者可以写多本书，一本书也可以有多个作者，双向的一对多，即多对多
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```sql
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create table author(
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id int primary key auto_increment,
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name varchar(20)
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);
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##这张表就存放作者表与书表的关系，即查询二者的关系查这表就可以了
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create table author2book(
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id int not null unique auto_increment,
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author_id int not null,
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book_id int not null,
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constraint fk_author foreign key(author_id) references author(id)
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on delete cascade
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on update cascade,
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constraint fk_book foreign key(book_id) references book(id)
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on delete cascade
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on update cascade,
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primary key(author_id,book_id)
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);
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##插入四个作者，id依次排开
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insert into author(name) values('zhangsan'),('lisi'),('wangwu'),('xuliu');
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##每个作者与自己的代表作如下
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zhangsan:
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九阳神功
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九阴真经
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九阴白骨爪
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独孤九剑
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降龙十巴掌
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葵花宝典
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lisi:
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九阳神功
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葵花宝典
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wangwu:
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独孤九剑
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降龙十巴掌
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葵花宝典
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xuliu:
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九阳神功
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insert into author2book(author_id,book_id) values
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(1,1),
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(1,2),
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(1,3),
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(1,4),
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(1,5),
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(1,6),
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(2,1),
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(2,6),
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(3,4),
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(3,5),
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(3,6),
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(4,1)
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;
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```
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**一对一**
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两张表：博客表和客户表
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一对一：一个用户只有一个博客
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```sql
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create table customer(
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id int primary key auto_increment,
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name varchar(20)
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)engine=innodb default charset=utf8;
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create table blog(
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id int primary key auto_increment,
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url varchar(50),
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name_id int unique,
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constraint fk_id foreign key(name_id) references customer(id)
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on delete cascade
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on update cascade
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)engine=innodb default charset=utf8;
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insert into customer(name) values
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('chensong'),('songge'),('songsong');
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insert into blog(url,name_id) values
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('xxxx',1),('yyyy',2),('zzzz',3);
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```
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#### 练习
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根据表结构合理设计表与表之间的主外键关系和约束，并完成表结构的创建。
|
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|
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|
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|
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参考答案
|
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|
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```sql
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create table class(
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cid int primary key auto_increment,
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caption varchar(20)
|
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)engine=innodb default charset=utf8;
|
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|
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create table student(
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sid int primary key auto_increment,
|
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sname varchar(20),
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gender enum('男','女'),
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class_id int,
|
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foreign key(class_id) references class(cid)
|
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)engine=innodb default charset=utf8;
|
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|
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create table teacher(
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tid int primary key auto_increment,
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tname varchar(20)
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)engine=innodb default charset=utf8;
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|
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create table course(
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cid int primary key auto_increment,
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cname varchar(20),
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teach_id int,
|
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foreign key(teach_id) references teacher(tid)
|
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)engine=innodb default charset=utf8;
|
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|
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create table score(
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sid int primary key auto_increment,
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student_id int,
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foreign key(student_id) references student(sid),
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corse_id int,
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foreign key(corse_id) references course(cid),
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number int
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)engine=innodb default charset=utf8;
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|
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insert into class(caption) value
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('三年一班'),
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('一年二班'),
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('三年二班');
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insert into student(sname, gender, class_id) value
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('东尼大木','男',1),
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('加藤鹰','男',1),
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('山形健','女',2);
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|
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insert into teacher(tname) value
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('波多'),
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('苍空'),
|
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('饭岛');
|
||
|
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insert into course(cname, teach_id) value
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||
('生物',1),
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('体育',1),
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||
('思想品德',2);
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insert into score(student_id, corse_id, number) value
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||
(1,1,60),
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||
(1,2,59),
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||
(2,2,100);
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select * from class;
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select * from student;
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select * from teacher;
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select * from course;
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select * from score;
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||
```
|
||
### MySQL支持的数据类型
|
||
#### 数值类型
|
||
MySQL支持所有标准SQL数值数据类型
|
||
这些类型包括严格数值数据类型(INTEGER、SMALLINT、DECIMAL和NUMERIC)，以及近似数值数据类型(FLOAT、REAL和DOUBLE PRECISION)。
|
||
关键字INT是INTEGER的同义词，关键字DEC是DECIMAL的同义词。
|
||
MySQL支持的整数类型有TINYINT、MEDIUMINT和BIGINT。下面的表显示了需要的每个整数类型的存储和范围。
|
||
对于小数的表示，MYSQL分为两种方式：浮点数和定点数。浮点数包括float(单精度)和double(双精度),而定点数只有decimal一种，在mysql中以字符串的形式存放，比浮点数更精确，适合用来表示货币等精度高的数据。
|
||
BIT数据类型保存位字段值，并且支持MyISAM、MEMORY、InnoDB和BDB表。
|
||
|
||
| | 类型 | 大小 | 范围（有符号） | 范围（无符号）unsigned约束 | 用途 |
|
||
| --- | --- | --- | --- | --- | --- |
|
||
| TINYINT | 1 字节 | (-128，127) | (0，255) | 小整数值 | |
|
||
| SMALLINT | 2 字节 | (-32 768，32 767) | (0，65 535) | 大整数值 | |
|
||
| MEDIUMINT | 3 字节 | (-8 388 608，8 388 607) | (0，16 777 215) | 大整数值 | |
|
||
| INT或INTEGER | 4 字节 | (-2 147 483 648，2 147 483 647) | (0，4 294 967 295) | 大整数值 | |
|
||
| BIGINT | 8 字节 | (-9 233 372 036 854 775 808，9 223 372 036 854 775 807) | (0，18 446 744 073 709 551 615) | 极大整数值 | |
|
||
| FLOAT | 4 字节
|
||
float(255,30) | (-3.402 823 466 E+38，-1.175 494 351 E-38)，0，(1.175 494 351 E-38，3.402 823 466 351 E+38) | 0，(1.175 494 351 E-38，3.402 823 466 E+38) | 单精度 | 浮点数值 |
|
||
| DOUBLE | 8 字节
|
||
double(255,30) | (-1.797 693 134 862 315 7 E+308，-2.225 073 858 507 201 4 E-308)，0，(2.225 073 858 507 201 4 E-308，1.797 693 134 862 315 7 E+308) | 0，(2.225 073 858 507 201 4 E-308，1.797 693 134 862 315 7 E+308) | 双精度 | 浮点数值 |
|
||
| DECIMAL | 对DECIMAL(M,D) ，如果M>D，为M+2否则为D+2
|
||
double(65,30) | 依赖于M和D的值 | 依赖于M和D的值 | 小数值 | |
|
||
|
||
```sql
|
||
## 创建表一个是默认宽度的int，一个是指定宽度的int(5)
|
||
mysql> create table t1 (id1 int,id2 int(5));
|
||
Query OK, 0 rows affected (0.02 sec)
|
||
|
||
## 像t1中插入数据1，1
|
||
mysql> insert into t1 values (1,1);
|
||
Query OK, 1 row affected (0.01 sec)
|
||
|
||
## 可以看出结果上并没有异常
|
||
mysql> select * from t1;
|
||
+------+------+
|
||
| id1 | id2 |
|
||
+------+------+
|
||
| 1 | 1 |
|
||
+------+------+
|
||
1 row in set (0.00 sec)
|
||
|
||
## 那么当我们插入了比宽度更大的值，会不会发生报错呢？
|
||
mysql> insert into t1 values (111111,111111);
|
||
Query OK, 1 row affected (0.00 sec)
|
||
|
||
## 答案是否定的，id2仍然显示了正确的数值，没有受到宽度限制的影响
|
||
mysql> select * from t1;
|
||
+------------+--------+
|
||
| id1 | id2 |
|
||
+------------+--------+
|
||
| 0000000001 | 00001 |
|
||
| 0000111111 | 111111 |
|
||
+------------+--------+
|
||
2 rows in set (0.00 sec)
|
||
|
||
## 修改id1字段 给字段添加一个unsigned表示无符号
|
||
mysql> alter table t1 modify id1 int unsigned;
|
||
Query OK, 0 rows affected (0.01 sec)
|
||
Records: 0 Duplicates: 0 Warnings: 0
|
||
|
||
mysql> desc t1;
|
||
+-------+------------------+------+-----+---------+-------+
|
||
| Field | Type | Null | Key | Default | Extra |
|
||
+-------+------------------+------+-----+---------+-------+
|
||
| id1 | int(10) unsigned | YES | | NULL | |
|
||
| id2 | int(5) | YES | | NULL | |
|
||
+-------+------------------+------+-----+---------+-------+
|
||
2 rows in set (0.01 sec)
|
||
|
||
## 当给id1添加的数据大于214748364时，可以顺利插入
|
||
mysql> insert into t1 values (2147483648,2147483647);
|
||
Query OK, 1 row affected (0.00 sec)
|
||
|
||
## 当给id2添加的数据大于214748364时，会报错
|
||
mysql> insert into t1 values (2147483647,2147483648);
|
||
ERROR 1264 (22003): Out of range value for column 'id2' at row 1
|
||
```
|
||
```sql
|
||
## 创建表的三个字段分别为float，double和decimal参数表示一共显示5位，小数部分占2位
|
||
mysql> create table t2 (id1 float(5,2),id2 double(5,2),id3 decimal(5,2));
|
||
Query OK, 0 rows affected (0.02 sec)
|
||
|
||
## 向表中插入1.23，结果正常
|
||
mysql> insert into t2 values (1.23,1.23,1.23);
|
||
Query OK, 1 row affected (0.00 sec)
|
||
|
||
mysql> select * from t2;
|
||
+------+------+------+
|
||
| id1 | id2 | id3 |
|
||
+------+------+------+
|
||
| 1.23 | 1.23 | 1.23 |
|
||
+------+------+------+
|
||
1 row in set (0.00 sec)
|
||
|
||
## 向表中插入1.234，会发现4都被截断了
|
||
mysql> insert into t2 values (1.234,1.234,1.234);
|
||
Query OK, 1 row affected, 1 warning (0.00 sec)
|
||
|
||
mysql> select * from t2;
|
||
+------+------+------+
|
||
| id1 | id2 | id3 |
|
||
+------+------+------+
|
||
| 1.23 | 1.23 | 1.23 |
|
||
| 1.23 | 1.23 | 1.23 |
|
||
+------+------+------+
|
||
2 rows in set (0.00 sec)
|
||
|
||
## 向表中插入1.235发现数据虽然被截断，但是遵循了四舍五入的规则
|
||
mysql> insert into t2 values (1.235,1.235,1.235);
|
||
Query OK, 1 row affected, 1 warning (0.00 sec)
|
||
|
||
mysql> select * from t2;
|
||
+------+------+------+
|
||
| id1 | id2 | id3 |
|
||
+------+------+------+
|
||
| 1.23 | 1.23 | 1.23 |
|
||
| 1.23 | 1.23 | 1.23 |
|
||
| 1.24 | 1.24 | 1.24 |
|
||
+------+------+------+
|
||
3 rows in set (0.00 sec)
|
||
|
||
## 建新表去掉参数约束
|
||
mysql> create table t3 (id1 float,id2 double,id3 decimal);
|
||
Query OK, 0 rows affected (0.02 sec)
|
||
|
||
## 分别插入1.234
|
||
mysql> insert into t3 values (1.234,1.234,1.234);
|
||
Query OK, 1 row affected, 1 warning (0.00 sec)
|
||
|
||
## 发现decimal默认值是(10,0)的整数
|
||
mysql> select * from t3;
|
||
+-------+-------+------+
|
||
| id1 | id2 | id3 |
|
||
+-------+-------+------+
|
||
| 1.234 | 1.234 | 1 |
|
||
+-------+-------+------+
|
||
1 row in set (0.00 sec)
|
||
|
||
## 当对小数位没有约束的时候，输入超长的小数，会发现float和double的区别
|
||
mysql> insert into t3 values (1.2355555555555555555,1.2355555555555555555,1.2355555555555555555555);
|
||
Query OK, 1 row affected, 1 warning (0.00 sec)
|
||
|
||
mysql> select * from t3;
|
||
+---------+--------------------+------+
|
||
| id1 | id2 | id3 |
|
||
+---------+--------------------+------+
|
||
| 1.234 | 1.234 | 1 |
|
||
| 1.23556 | 1.2355555555555555 | 1 |
|
||
+---------+--------------------+------+
|
||
2 rows in set (0.00 sec)
|
||
```
|
||
#### 日期和时间类型
|
||
表示时间值的日期和时间类型为DATETIME、DATE、TIMESTAMP、TIME和YEAR。
|
||
每个时间类型有一个有效值范围和一个"零"值，当指定不合法的MySQL不能表示的值时使用"零"值。
|
||
TIMESTAMP类型有专有的自动更新特性，将在后面描述。
|
||
|
||
| 类型 | 大小 | (字节) | 范围 | 格式 | 用途 |
|
||
| --- | --- | --- | --- | --- | --- |
|
||
| DATE | 3 | 1000-01-01/9999-12-31 | YYYY-MM-DD | 年月日 | |
|
||
| TIME | 3 | '-838:59:59'/'838:59:59' | HH:MM:SS | 时分秒 | |
|
||
| YEAR | 1 | 1901/2155 | YYYY | 年份值 | |
|
||
| DATETIME | 8 | 1000-01-01 00:00:00/9999-12-31 23:59:59 | YYYY-MM-DD HH:MM:SS | 年月日时分秒 | |
|
||
| TIMESTAMP | 4 | 1970-01-01 00:00:00/2038
|
||
结束时间是第 **2147483647** 秒，北京时间 **2038-1-19 11:14:07**，格林尼治时间 2038年1月19日 凌晨 03:14:07 | YYYYMMDD HHMMSS | 混合日期和时间值，时间戳 | |
|
||
|
||
```sql
|
||
MariaDB [db2]> create table time(d date,t time,dt datetime);
|
||
Query OK, 0 rows affected (0.00 sec)
|
||
|
||
MariaDB [db2]> desc time;
|
||
+-------+----------+------+-----+---------+-------+
|
||
| Field | Type | Null | Key | Default | Extra |
|
||
+-------+----------+------+-----+---------+-------+
|
||
| d | date | YES | | NULL | |
|
||
| t | time | YES | | NULL | |
|
||
| dt | datetime | YES | | NULL | |
|
||
+-------+----------+------+-----+---------+-------+
|
||
3 rows in set (0.00 sec)
|
||
|
||
MariaDB [db2]> insert into time values(now(),now(),now());
|
||
Query OK, 1 row affected, 2 warnings (0.00 sec)
|
||
|
||
MariaDB [db2]> select * from time;
|
||
+------------+----------+---------------------+
|
||
| d | t | dt |
|
||
+------------+----------+---------------------+
|
||
| 2019-02-27 | 11:29:32 | 2019-02-27 11:29:32 |
|
||
+------------+----------+---------------------+
|
||
1 row in set (0.00 sec)
|
||
|
||
MariaDB [db2]> insert into time values (null,null,null);
|
||
Query OK, 1 row affected (0.00 sec)
|
||
|
||
MariaDB [db2]> select * from time;
|
||
+------------+----------+---------------------+
|
||
| d | t | dt |
|
||
+------------+----------+---------------------+
|
||
| 2019-02-27 | 11:29:32 | 2019-02-27 11:29:32 |
|
||
| NULL | NULL | NULL |
|
||
+------------+----------+---------------------+
|
||
2 rows in set (0.00 sec)
|
||
```
|
||
```sql
|
||
mysql> create table t5 (id1 timestamp);
|
||
Query OK, 0 rows affected (0.02 sec)
|
||
|
||
mysql> desc t5;
|
||
+-------+-----------+------+-----+-------------------+-----------------------------+
|
||
| Field | Type | Null | Key | Default | Extra |
|
||
+-------+-----------+------+-----+-------------------+-----------------------------+
|
||
| id1 | timestamp | NO | | CURRENT_TIMESTAMP | on update CURRENT_TIMESTAMP |
|
||
+-------+-----------+------+-----+-------------------+-----------------------------+
|
||
1 row in set (0.00 sec)
|
||
|
||
## 插入数据null，会自动插入当前时间的时间
|
||
mysql> insert into t5 values (null);
|
||
Query OK, 1 row affected (0.00 sec)
|
||
|
||
mysql> select * from t5;
|
||
+---------------------+
|
||
| id1 |
|
||
+---------------------+
|
||
| 2019-02-21 14:56:50 |
|
||
+---------------------+
|
||
1 row in set (0.00 sec)
|
||
|
||
##添加一列 默认值是'0000-00-00 00:00:00'
|
||
mysql> alter table t5 add id2 timestamp;
|
||
Query OK, 0 rows affected (0.02 sec)
|
||
Records: 0 Duplicates: 0 Warnings: 0
|
||
|
||
mysql> show create table t5 \G;
|
||
*************************** 1. row ***************************
|
||
Table: t5
|
||
Create Table: CREATE TABLE `t5` (
|
||
`id1` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP,
|
||
`id2` timestamp NOT NULL DEFAULT '0000-00-00 00:00:00'
|
||
) ENGINE=InnoDB DEFAULT CHARSET=utf8
|
||
1 row in set (0.00 sec)
|
||
|
||
ERROR:
|
||
No query specified
|
||
|
||
## 手动修改新的列默认值为当前时间
|
||
mysql> alter table t5 modify id2 timestamp default current_timestamp;
|
||
Query OK, 0 rows affected (0.02 sec)
|
||
Records: 0 Duplicates: 0 Warnings: 0
|
||
|
||
mysql> show create table t5 \G;
|
||
*************************** 1. row ***************************
|
||
Table: t5
|
||
Create Table: CREATE TABLE `t5` (
|
||
`id1` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP,
|
||
`id2` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP
|
||
) ENGINE=InnoDB DEFAULT CHARSET=utf8
|
||
1 row in set (0.00 sec)
|
||
|
||
ERROR:
|
||
No query specified
|
||
|
||
mysql> insert into t5 values (null,null);
|
||
Query OK, 1 row affected (0.01 sec)
|
||
|
||
mysql> select * from t5;
|
||
+---------------------+---------------------+
|
||
| id1 | id2 |
|
||
+---------------------+---------------------+
|
||
| 2019-02-21 14:56:50 | 0000-00-00 00:00:00 |
|
||
| 2019-02-21 14:59:31 | 2019-02-21 14:59:31 |
|
||
+---------------------+---------------------+
|
||
2 rows in set (0.00 sec)
|
||
```
|
||
```sql
|
||
mysql> create table t6 (t1 timestamp);
|
||
Query OK, 0 rows affected (0.02 sec)
|
||
|
||
mysql> desc t6;
|
||
+-------+-----------+------+-----+-------------------+-----------------------------+
|
||
| Field | Type | Null | Key | Default | Extra |
|
||
+-------+-----------+------+-----+-------------------+-----------------------------+
|
||
| t1 | timestamp | NO | | CURRENT_TIMESTAMP | on update CURRENT_TIMESTAMP |
|
||
+-------+-----------+------+-----+-------------------+-----------------------------+
|
||
1 row in set (0.01 sec)
|
||
|
||
mysql> insert into t6 values (19700101080001);
|
||
Query OK, 1 row affected (0.00 sec)
|
||
|
||
mysql> select * from t6;
|
||
+---------------------+
|
||
| t1 |
|
||
+---------------------+
|
||
| 1970-01-01 08:00:01 |
|
||
+---------------------+
|
||
1 row in set (0.00 sec)
|
||
## timestamp时间的下限是19700101080001
|
||
mysql> insert into t6 values (19700101080000);
|
||
ERROR 1292 (22007): Incorrect datetime value: '19700101080000' for column 't1' at row 1
|
||
|
||
mysql> insert into t6 values ('2038-01-19 11:14:07');
|
||
Query OK, 1 row affected (0.00 sec)
|
||
## timestamp时间的上限是2038-01-19 11:14:07
|
||
mysql> insert into t6 values ('2038-01-19 11:14:08');
|
||
ERROR 1292 (22007): Incorrect datetime value: '2038-01-19 11:14:08' for column 't1' at row 1
|
||
mysql>
|
||
```
|
||
```java
|
||
mysql> create table t7 (y year);
|
||
Query OK, 0 rows affected (0.02 sec)
|
||
|
||
mysql> insert into t7 values (2019);
|
||
Query OK, 1 row affected (0.00 sec)
|
||
|
||
mysql> select * from t7;
|
||
+------+
|
||
| y |
|
||
+------+
|
||
| 2019 |
|
||
+------+
|
||
1 row in set (0.00 sec)
|
||
```
|
||
```sql
|
||
mysql> create table t8 (dt datetime);
|
||
Query OK, 0 rows affected (0.01 sec)
|
||
|
||
mysql> insert into t8 values ('2019-2-26 12:20:10');
|
||
Query OK, 1 row affected (0.01 sec)
|
||
|
||
mysql> insert into t8 values ('2019/2/26 12+20+10');
|
||
Query OK, 1 row affected (0.00 sec)
|
||
|
||
mysql> insert into t8 values ('20190226122010');
|
||
Query OK, 1 row affected (0.00 sec)
|
||
|
||
mysql> insert into t8 values (20190926122010);
|
||
Query OK, 1 row affected (0.00 sec)
|
||
|
||
mysql> select * from t8;
|
||
+---------------------+
|
||
| dt |
|
||
+---------------------+
|
||
| 2019-02-26 12:20:10 |
|
||
| 2019-02-26 12:20:10 |
|
||
| 2019-02-26 12:20:10 |
|
||
| 2019-02-26 12:20:10 |
|
||
+---------------------+
|
||
4 rows in set (0.00 sec)
|
||
```
|
||
#### 字符串类型
|
||
字符串类型指CHAR、VARCHAR、BINARY、VARBINARY、BLOB、TEXT、ENUM和SET。该节描述了这些类型如何工作以及如何在查询中使用这些类型。
|
||
|
||
| 类型 | 大小 | 用途 |
|
||
| --- | --- | --- |
|
||
| CHAR | 0-255字节 | 定长字符串 |
|
||
| VARCHAR | 0-65535 字节 | 变长字符串 |
|
||
| TINYBLOB | 0-255字节 | 不超过 255 个字符的二进制字符串 |
|
||
| TINYTEXT | 0-255字节 | 短文本字符串 |
|
||
| BLOB | 0-65 535字节 | 二进制形式的长文本数据 |
|
||
| TEXT | 0-65 535字节 | 长文本数据 |
|
||
| MEDIUMBLOB | 0-16 777 215字节 | 二进制形式的中等长度文本数据 |
|
||
| MEDIUMTEXT | 0-16 777 215字节 | 中等长度文本数据 |
|
||
| LONGBLOB | 0-4 294 967 295字节 | 二进制形式的极大文本数据 |
|
||
| LONGTEXT | 0-4 294 967 295字节 | 极大文本数据 |
|
||
|
||
CHAR 和 VARCHAR 类型类似，但它们保存和检索的方式不同。它们的最大长度和是否尾部空格被保留等方面也不同。在存储或检索过程中不进行大小写转换。
|
||
CHAR列的长度固定为创建表是声明的长度,范围(0-255);而VARCHAR的值是可变长字符串范围(0-65535)。
|
||
```sql
|
||
mysql> create table t9 (v varchar(4),c char(4));
|
||
Query OK, 0 rows affected (0.01 sec)
|
||
|
||
mysql> insert into t9 values ('ab ','ab ');
|
||
Query OK, 1 row affected (0.00 sec)
|
||
|
||
## 在检索的时候char数据类型会去掉空格
|
||
mysql> select * from t9;
|
||
+------+------+
|
||
| v | c |
|
||
+------+------+
|
||
| ab | ab |
|
||
+------+------+
|
||
1 row in set (0.00 sec)
|
||
|
||
## 来看看对查询结果计算的长度
|
||
mysql> select length(v),length(c) from t9;
|
||
+-----------+-----------+
|
||
| length(v) | length(c) |
|
||
+-----------+-----------+
|
||
| 4 | 2 |
|
||
+-----------+-----------+
|
||
1 row in set (0.00 sec)
|
||
|
||
## 给结果拼上一个加号会更清楚
|
||
mysql> select concat(v,'+'),concat(c,'+') from t9;
|
||
+---------------+---------------+
|
||
| concat(v,'+') | concat(c,'+') |
|
||
+---------------+---------------+
|
||
| ab + | ab+ |
|
||
+---------------+---------------+
|
||
1 row in set (0.00 sec)
|
||
|
||
## 当存储的长度超出定义的长度，会截断
|
||
mysql> insert into t9 values ('abcd ','abcd ');
|
||
Query OK, 1 row affected, 1 warning (0.01 sec)
|
||
|
||
mysql> select * from t9;
|
||
+------+------+
|
||
| v | c |
|
||
+------+------+
|
||
| ab | ab |
|
||
| abcd | abcd |
|
||
+------+------+
|
||
2 rows in set (0.00 sec)
|
||
```
|
||
BINARY 和 VARBINARY 类似于 CHAR 和 VARCHAR，不同的是它们包含二进制字符串而不要非二进制字符串。也就是说，它们包含字节字符串而不是字符字符串。这说明它们没有字符集，并且排序和比较基于列值字节的数值值。
|
||
BLOB 是一个二进制大对象，可以容纳可变数量的数据。有 4 种 BLOB 类型：TINYBLOB、BLOB、MEDIUMBLOB 和 LONGBLOB。它们区别在于可容纳存储范围不同。
|
||
有 4 种 TEXT 类型：TINYTEXT、TEXT、MEDIUMTEXT 和 LONGTEXT。对应的这 4 种 BLOB 类型，可存储的最大长度不同，可根据实际情况选择。
|
||
#### ENUM和SET类型
|
||
ENUM中文名称叫枚举类型，它的值范围需要在创建表时通过枚举方式显示。ENUM**只允许从值集合中选取单个值，而不能一次取多个值**。
|
||
SET和ENUM非常相似，也是一个字符串对象，里面可以包含0-64个成员。根据成员的不同，存储上也有所不同。set类型可以**允许值集合中任意选择1或多个元素进行组合**。对超出范围的内容将不允许注入，而对重复的值将进行自动去重。
|
||
|
||
| 类型 | 大小 | 用途 |
|
||
| --- | --- | --- |
|
||
| ENUM | 对1-255个成员的枚举需要1个字节存储;
|
||
对于255-65535个成员，需要2个字节存储;
|
||
最多允许65535个成员。 | 单选：选择性别 |
|
||
| SET | 1-8个成员的集合，占1个字节
|
||
9-16个成员的集合，占2个字节
|
||
17-24个成员的集合，占3个字节
|
||
25-32个成员的集合，占4个字节
|
||
33-64个成员的集合，占8个字节 | 多选：兴趣爱好 |
|
||
|
||
```sql
|
||
mysql> create table t10 (name char(20),gender enum('female','male'));
|
||
Query OK, 0 rows affected (0.01 sec)
|
||
|
||
## 选择enum('female','male')中的一项作为gender的值，可以正常插入
|
||
mysql> insert into t10 values ('zhangsan','male');
|
||
Query OK, 1 row affected (0.00 sec)
|
||
|
||
## 不能同时插入'male,female'两个值，也不能插入不属于'male,female'的值
|
||
mysql> insert into t10 values ('zhangsan','male,female');
|
||
ERROR 1265 (01000): Data truncated for column 'gender' at row 1
|
||
|
||
mysql> create table t11 (name char(20),hobby set('抽烟','喝酒','烫头','翻车'));
|
||
Query OK, 0 rows affected (0.01 sec)
|
||
|
||
## 可以任意选择set('抽烟','喝酒','烫头','翻车')中的项，并自带去重功能
|
||
mysql> insert into t11 values ('zhangsan','烫头,喝酒,烫头');
|
||
Query OK, 1 row affected (0.01 sec)
|
||
|
||
mysql> select * from t11;
|
||
+----------+---------------+
|
||
| name | hobby |
|
||
+----------+---------------+
|
||
| zhangsan | 喝酒,烫头 |
|
||
+----------+---------------+
|
||
1 row in set (0.00 sec)
|
||
|
||
## 不能选择不属于set('抽烟','喝酒','烫头','翻车')中的项，
|
||
mysql> insert into t11 values ('zhangsan','烫头,翻车,看妹子');
|
||
ERROR 1265 (01000): Data truncated for column 'hobby' at row 1
|
||
```
|
||
### 表的完整性约束
|
||
#### 概述
|
||
为了防止不符合规范的数据进入数据库，在用户对数据进行插入、修改、删除等操作时，DBMS自动按照一定的约束条件对数据进行监测，使不符合规范的数据不能进入数据库，以确保数据库中存储的数据正确、有效、相容。
|
||
约束条件与数据类型的宽度一样，都是可选参数，主要分为以下几种：
|
||
1. NOT NULL ：非空约束，指定某列不能为空；
|
||
2. UNIQUE : 唯一约束，指定某列或者几列组合不能重复
|
||
3. PRIMARY KEY ：主键，指定该列的值可以唯一地标识该列记录
|
||
4. FOREIGN KEY ：外键，指定该行记录从属于主表中的一条记录，主要用于参照完整性
|
||
#### NOT NULL
|
||
是否可空，null表示空，非字符串
|
||
not null - 不可空
|
||
null - 可空(默认)
|
||
```sql
|
||
mysql> create table t12 (id int not null);
|
||
Query OK, 0 rows affected (0.02 sec)
|
||
|
||
mysql> select * from t12;
|
||
Empty set (0.00 sec)
|
||
|
||
mysql> desc t12;
|
||
+-------+---------+------+-----+---------+-------+
|
||
| Field | Type | Null | Key | Default | Extra |
|
||
+-------+---------+------+-----+---------+-------+
|
||
| id | int(11) | NO | | NULL | |
|
||
+-------+---------+------+-----+---------+-------+
|
||
1 row in set (0.00 sec)
|
||
|
||
##不能向id列插入空元素。
|
||
mysql> insert into t12 values (null);
|
||
ERROR 1048 (23000): Column 'id' cannot be null
|
||
|
||
mysql> insert into t12 values (1);
|
||
Query OK, 1 row affected (0.01 sec)
|
||
```
|
||
#### DEFAULT
|
||
约束某一列不为空，如果这一列中经常有重复的内容，就需要我们频繁的插入，这样会给我们的操作带来新的负担，于是就出现了默认值的概念。
|
||
默认值，创建列时可以指定默认值，当插入数据时如果未主动设置，则自动添加默认值
|
||
```sql
|
||
mysql> create table t13 (id1 int not null,id2 int not null default 222);
|
||
Query OK, 0 rows affected (0.01 sec)
|
||
|
||
mysql> desc t13;
|
||
+-------+---------+------+-----+---------+-------+
|
||
| Field | Type | Null | Key | Default | Extra |
|
||
+-------+---------+------+-----+---------+-------+
|
||
| id1 | int(11) | NO | | NULL | |
|
||
| id2 | int(11) | NO | | 222 | |
|
||
+-------+---------+------+-----+---------+-------+
|
||
2 rows in set (0.01 sec)
|
||
|
||
## 只向id1字段添加值，会发现id2字段会使用默认值填充
|
||
mysql> insert into t13 (id1) values (111);
|
||
Query OK, 1 row affected (0.00 sec)
|
||
|
||
mysql> select * from t13;
|
||
+-----+-----+
|
||
| id1 | id2 |
|
||
+-----+-----+
|
||
| 111 | 222 |
|
||
+-----+-----+
|
||
1 row in set (0.00 sec)
|
||
|
||
## id1字段不能为空，所以不能单独向id2字段填充值；
|
||
mysql> insert into t13 (id2) values (223);
|
||
ERROR 1364 (HY000): Field 'id1' doesn't have a default value
|
||
|
||
## 向id1，id2中分别填充数据，id2的填充数据会覆盖默认值
|
||
mysql> insert into t13 (id1,id2) values (112,223);
|
||
Query OK, 1 row affected (0.00 sec)
|
||
|
||
mysql> select * from t13;
|
||
+-----+-----+
|
||
| id1 | id2 |
|
||
+-----+-----+
|
||
| 111 | 222 |
|
||
| 112 | 223 |
|
||
+-----+-----+
|
||
2 rows in set (0.00 sec)
|
||
```
|
||
设置严格模式:
|
||
|
||
- 不支持对not null字段插入null值
|
||
- 不支持对自增长字段插入null值
|
||
- 不支持text字段有默认值
|
||
```sql
|
||
直接在mysql中生效(重启失效):
|
||
mysql>set sql_mode="STRICT_TRANS_TABLES,NO_AUTO_CREATE_USER,NO_ENGINE_SUBSTITUTION";
|
||
|
||
配置文件添加(永久失效)：
|
||
sql-mode="STRICT_TRANS_TABLES,NO_AUTO_CREATE_USER,NO_ENGINE_SUBSTITUTION"
|
||
```
|
||
#### UNIQUE
|
||
唯一约束，指定某列或者几列组合不能重复
|
||
```sql
|
||
方法一：
|
||
create table department1(
|
||
id int,
|
||
name varchar(20) unique,
|
||
comment varchar(100)
|
||
);
|
||
|
||
|
||
方法二：
|
||
create table department2(
|
||
id int,
|
||
name varchar(20),
|
||
comment varchar(100),
|
||
unique(name)
|
||
);
|
||
|
||
|
||
mysql> insert into department1 values(1,'IT','技术');
|
||
Query OK, 1 row affected (0.00 sec)
|
||
mysql> insert into department1 values(1,'IT','技术');
|
||
ERROR 1062 (23000): Duplicate entry 'IT' for key 'name'
|
||
```
|
||
```sql
|
||
mysql> create table t1(id int not null unique);
|
||
Query OK, 0 rows affected (0.02 sec)
|
||
|
||
mysql> desc t1;
|
||
+-------+---------+------+-----+---------+-------+
|
||
| Field | Type | Null | Key | Default | Extra |
|
||
+-------+---------+------+-----+---------+-------+
|
||
| id | int(11) | NO | PRI | NULL | |
|
||
+-------+---------+------+-----+---------+-------+
|
||
1 row in set (0.00 sec)
|
||
```
|
||
```sql
|
||
create table service(
|
||
id int primary key auto_increment,
|
||
name varchar(20),
|
||
host varchar(15) not null,
|
||
port int not null,
|
||
unique(host,port) #联合唯一
|
||
);
|
||
|
||
mysql> insert into service values
|
||
-> (1,'nginx','192.168.0.10',80),
|
||
-> (2,'haproxy','192.168.0.20',80),
|
||
-> (3,'mysql','192.168.0.30',3306)
|
||
-> ;
|
||
Query OK, 3 rows affected (0.01 sec)
|
||
Records: 3 Duplicates: 0 Warnings: 0
|
||
|
||
mysql> insert into service(name,host,port) values('nginx','192.168.0.10',80);
|
||
ERROR 1062 (23000): Duplicate entry '192.168.0.10-80' for key 'host'
|
||
```
|
||
#### PRIMARY KEY
|
||
主键为了保证表中的每一条数据的该字段都是表格中的唯一值。换言之，它是用来独一无二地确认一个表格中的每一行数据。
|
||
主键可以包含一个字段或多个字段。当主键包含多个栏位时，称为组合键 (Composite Key),也可以叫联合主键。
|
||
主键可以在建置新表格时设定 (运用 CREATE TABLE 语句)，或是以改变现有的表格架构方式设定 (运用 ALTER TABLE)。
|
||
主键必须唯一，主键值非空；可以是单一字段，也可以是多字段组合。
|
||
|
||
1. 单字段主键
|
||
```sql
|
||
============单列做主键===============
|
||
##方法一：not null+unique
|
||
create table department1(
|
||
id int not null unique, #主键
|
||
name varchar(20) not null unique,
|
||
comment varchar(100)
|
||
);
|
||
|
||
mysql> desc department1;
|
||
+---------+--------------+------+-----+---------+-------+
|
||
| Field | Type | Null | Key | Default | Extra |
|
||
+---------+--------------+------+-----+---------+-------+
|
||
| id | int(11) | NO | PRI | NULL | |
|
||
| name | varchar(20) | NO | UNI | NULL | |
|
||
| comment | varchar(100) | YES | | NULL | |
|
||
+---------+--------------+------+-----+---------+-------+
|
||
rows in set (0.01 sec)
|
||
|
||
##方法二：在某一个字段后用primary key
|
||
create table department2(
|
||
id int primary key, #主键
|
||
name varchar(20),
|
||
comment varchar(100)
|
||
);
|
||
|
||
mysql> desc department2;
|
||
+---------+--------------+------+-----+---------+-------+
|
||
| Field | Type | Null | Key | Default | Extra |
|
||
+---------+--------------+------+-----+---------+-------+
|
||
| id | int(11) | NO | PRI | NULL | |
|
||
| name | varchar(20) | YES | | NULL | |
|
||
| comment | varchar(100) | YES | | NULL | |
|
||
+---------+--------------+------+-----+---------+-------+
|
||
rows in set (0.00 sec)
|
||
|
||
##方法三：在所有字段后单独定义primary key
|
||
create table department3(
|
||
id int,
|
||
name varchar(20),
|
||
comment varchar(100),
|
||
primary key(id); #创建主键并为其命名pk_name
|
||
|
||
mysql> desc department3;
|
||
+---------+--------------+------+-----+---------+-------+
|
||
| Field | Type | Null | Key | Default | Extra |
|
||
+---------+--------------+------+-----+---------+-------+
|
||
| id | int(11) | NO | PRI | NULL | |
|
||
| name | varchar(20) | YES | | NULL | |
|
||
| comment | varchar(100) | YES | | NULL | |
|
||
+---------+--------------+------+-----+---------+-------+
|
||
rows in set (0.01 sec)
|
||
|
||
## 方法四：给已经建成的表添加主键约束
|
||
mysql> create table department4(
|
||
-> id int,
|
||
-> name varchar(20),
|
||
-> comment varchar(100));
|
||
Query OK, 0 rows affected (0.01 sec)
|
||
|
||
mysql> desc department4;
|
||
+---------+--------------+------+-----+---------+-------+
|
||
| Field | Type | Null | Key | Default | Extra |
|
||
+---------+--------------+------+-----+---------+-------+
|
||
| id | int(11) | YES | | NULL | |
|
||
| name | varchar(20) | YES | | NULL | |
|
||
| comment | varchar(100) | YES | | NULL | |
|
||
+---------+--------------+------+-----+---------+-------+
|
||
3 rows in set (0.01 sec)
|
||
|
||
mysql> alter table department4 modify id int primary key;
|
||
Query OK, 0 rows affected (0.02 sec)
|
||
Records: 0 Duplicates: 0 Warnings: 0
|
||
|
||
mysql> desc department4;
|
||
+---------+--------------+------+-----+---------+-------+
|
||
| Field | Type | Null | Key | Default | Extra |
|
||
+---------+--------------+------+-----+---------+-------+
|
||
| id | int(11) | NO | PRI | NULL | |
|
||
| name | varchar(20) | YES | | NULL | |
|
||
| comment | varchar(100) | YES | | NULL | |
|
||
+---------+--------------+------+-----+---------+-------+
|
||
3 rows in set (0.01 sec)
|
||
```
|
||
|
||
2. 多字段主键
|
||
```sql
|
||
==================多列做主键================
|
||
create table service(
|
||
ip varchar(15),
|
||
port char(5),
|
||
service_name varchar(10) not null,
|
||
primary key(ip,port)
|
||
);
|
||
|
||
|
||
mysql> desc service;
|
||
+--------------+-------------+------+-----+---------+-------+
|
||
| Field | Type | Null | Key | Default | Extra |
|
||
+--------------+-------------+------+-----+---------+-------+
|
||
| ip | varchar(15) | NO | PRI | NULL | |
|
||
| port | char(5) | NO | PRI | NULL | |
|
||
| service_name | varchar(10) | NO | | NULL | |
|
||
+--------------+-------------+------+-----+---------+-------+
|
||
3 rows in set (0.00 sec)
|
||
|
||
mysql> insert into service values
|
||
-> ('172.16.45.10','3306','mysqld'),
|
||
-> ('172.16.45.11','3306','mariadb')
|
||
-> ;
|
||
Query OK, 2 rows affected (0.00 sec)
|
||
Records: 2 Duplicates: 0 Warnings: 0
|
||
|
||
mysql> insert into service values ('172.16.45.10','3306','nginx');
|
||
ERROR 1062 (23000): Duplicate entry '172.16.45.10-3306' for key 'PRIMARY'
|
||
```
|
||
#### AUTO_INCREMENT
|
||
约束字段为自动增长，被约束的字段必须同时被key约束
|
||
```sql
|
||
##不指定id，则自动增长
|
||
create table student(
|
||
id int primary key auto_increment,
|
||
name varchar(20),
|
||
sex enum('male','female') default 'male'
|
||
);
|
||
|
||
mysql> desc student;
|
||
+-------+-----------------------+------+-----+---------+----------------+
|
||
| Field | Type | Null | Key | Default | Extra |
|
||
+-------+-----------------------+------+-----+---------+----------------+
|
||
| id | int(11) | NO | PRI | NULL | auto_increment |
|
||
| name | varchar(20) | YES | | NULL | |
|
||
| sex | enum('male','female') | YES | | male | |
|
||
+-------+-----------------------+------+-----+---------+----------------+
|
||
mysql> insert into student(name) values
|
||
-> ('egon'),
|
||
-> ('alex')
|
||
-> ;
|
||
|
||
mysql> select * from student;
|
||
+----+------+------+
|
||
| id | name | sex |
|
||
+----+------+------+
|
||
| 1 | egon | male |
|
||
| 2 | alex | male |
|
||
+----+------+------+
|
||
|
||
|
||
##也可以指定id
|
||
mysql> insert into student values(4,'asb','female');
|
||
Query OK, 1 row affected (0.00 sec)
|
||
|
||
mysql> insert into student values(7,'wsb','female');
|
||
Query OK, 1 row affected (0.00 sec)
|
||
|
||
mysql> select * from student;
|
||
+----+------+--------+
|
||
| id | name | sex |
|
||
+----+------+--------+
|
||
| 1 | egon | male |
|
||
| 2 | alex | male |
|
||
| 4 | asb | female |
|
||
| 7 | wsb | female |
|
||
+----+------+--------+
|
||
|
||
|
||
##对于自增的字段，在用delete删除后，再插入值，该字段仍按照删除前的位置继续增长
|
||
mysql> delete from student;
|
||
Query OK, 4 rows affected (0.00 sec)
|
||
|
||
mysql> select * from student;
|
||
Empty set (0.00 sec)
|
||
|
||
mysql> insert into student(name) values('ysb');
|
||
mysql> select * from student;
|
||
+----+------+------+
|
||
| id | name | sex |
|
||
+----+------+------+
|
||
| 8 | ysb | male |
|
||
+----+------+------+
|
||
|
||
##应该用truncate清空表，比起delete一条一条地删除记录，truncate是直接清空表，在删除大表时用它
|
||
mysql> truncate student;
|
||
Query OK, 0 rows affected (0.01 sec)
|
||
|
||
mysql> insert into student(name) values('egon');
|
||
Query OK, 1 row affected (0.01 sec)
|
||
|
||
mysql> select * from student;
|
||
+----+------+------+
|
||
| id | name | sex |
|
||
+----+------+------+
|
||
| 1 | egon | male |
|
||
+----+------+------+
|
||
row in set (0.00 sec)
|
||
```
|
||
知识扩展
|
||
```sql
|
||
##在创建完表后，修改自增字段的起始值
|
||
mysql> create table student(
|
||
-> id int primary key auto_increment,
|
||
-> name varchar(20),
|
||
-> sex enum('male','female') default 'male'
|
||
-> );
|
||
|
||
mysql> alter table student auto_increment=3;
|
||
|
||
mysql> show create table student;
|
||
.......
|
||
ENGINE=InnoDB AUTO_INCREMENT=3 DEFAULT CHARSET=utf8
|
||
|
||
mysql> insert into student(name) values('egon');
|
||
Query OK, 1 row affected (0.01 sec)
|
||
|
||
mysql> select * from student;
|
||
+----+------+------+
|
||
| id | name | sex |
|
||
+----+------+------+
|
||
| 3 | egon | male |
|
||
+----+------+------+
|
||
row in set (0.00 sec)
|
||
|
||
mysql> show create table student;
|
||
.......
|
||
ENGINE=InnoDB AUTO_INCREMENT=4 DEFAULT CHARSET=utf8
|
||
|
||
|
||
##也可以创建表时指定auto_increment的初始值，注意初始值的设置为表选项，应该放到括号外
|
||
create table student(
|
||
id int primary key auto_increment,
|
||
name varchar(20),
|
||
sex enum('male','female') default 'male'
|
||
)auto_increment=3;
|
||
|
||
|
||
|
||
|
||
##设置步长
|
||
sqlserver：自增步长
|
||
基于表级别
|
||
create table t1（
|
||
id int。。。
|
||
）engine=innodb,auto_increment=2 步长=2 default charset=utf8
|
||
|
||
mysql自增的步长：
|
||
show session variables like 'auto_inc%';
|
||
|
||
#基于会话级别
|
||
set session auto_increment_increment=2 #修改会话级别的步长
|
||
|
||
#基于全局级别的
|
||
set global auto_increment_increment=2 #修改全局级别的步长（所有会话都生效）
|
||
|
||
|
||
##！！！注意了注意了注意了！！！
|
||
If the value of auto_increment_offset is greater than that of auto_increment_increment, the value of auto_increment_offset is ignored.
|
||
翻译：如果auto_increment_offset的值大于auto_increment_increment的值，则auto_increment_offset的值会被忽略 ，这相当于第一步步子就迈大了，扯着了蛋
|
||
比如：设置auto_increment_offset=3，auto_increment_increment=2
|
||
|
||
|
||
|
||
|
||
mysql> set global auto_increment_increment=5;
|
||
Query OK, 0 rows affected (0.00 sec)
|
||
|
||
mysql> set global auto_increment_offset=3;
|
||
Query OK, 0 rows affected (0.00 sec)
|
||
|
||
mysql> show variables like 'auto_incre%'; #需要退出重新登录
|
||
+--------------------------+-------+
|
||
| Variable_name | Value |
|
||
+--------------------------+-------+
|
||
| auto_increment_increment | 1 |
|
||
| auto_increment_offset | 1 |
|
||
+--------------------------+-------+
|
||
|
||
|
||
|
||
create table student(
|
||
id int primary key auto_increment,
|
||
name varchar(20),
|
||
sex enum('male','female') default 'male'
|
||
);
|
||
|
||
mysql> insert into student(name) values('egon1'),('egon2'),('egon3');
|
||
mysql> select * from student;
|
||
+----+-------+------+
|
||
| id | name | sex |
|
||
+----+-------+------+
|
||
| 3 | egon1 | male |
|
||
| 8 | egon2 | male |
|
||
| 13 | egon3 | male |
|
||
+----+-------+------+
|
||
|
||
步长:auto_increment_increment,起始偏移量:auto_increment_offset
|
||
```
|
||
#### FOREIKEY
|
||
表 ：
|
||
假设我们要描述所有公司的员工，需要描述的属性有这些 ： 工号 姓名 部门
|
||
公司有3个部门，但是有1个亿的员工，那意味着部门这个字段需要重复存储，部门名字越长，越浪费
|
||
解决方法： 我们完全可以定义一个部门表 然后让员工信息表关联该表，如何关联，即foreign key
|
||
```sql
|
||
mysql> create table departments (dep_id int(4),dep_name varchar(11));
|
||
Query OK, 0 rows affected (0.02 sec)
|
||
|
||
mysql> desc departments;
|
||
+----------+-------------+------+-----+---------+-------+
|
||
| Field | Type | Null | Key | Default | Extra |
|
||
+----------+-------------+------+-----+---------+-------+
|
||
| dep_id | int(4) | YES | | NULL | |
|
||
| dep_name | varchar(11) | YES | | NULL | |
|
||
+----------+-------------+------+-----+---------+-------+
|
||
2 rows in set (0.00 sec)
|
||
|
||
## 创建外键不成功
|
||
mysql> create table staff_info (s_id int,name varchar(20),dep_id int,foreign key(dep_id) references departments(dep_id));
|
||
ERROR 1215 (HY000): Cannot add foreign key
|
||
|
||
## 设置dep_id非空，仍然不能成功创建外键
|
||
mysql> alter table departments modify dep_id int(4) not null;
|
||
Query OK, 0 rows affected (0.02 sec)
|
||
Records: 0 Duplicates: 0 Warnings: 0
|
||
|
||
mysql> desc departments;
|
||
+----------+-------------+------+-----+---------+-------+
|
||
| Field | Type | Null | Key | Default | Extra |
|
||
+----------+-------------+------+-----+---------+-------+
|
||
| dep_id | int(4) | NO | | NULL | |
|
||
| dep_name | varchar(11) | YES | | NULL | |
|
||
+----------+-------------+------+-----+---------+-------+
|
||
2 rows in set (0.00 sec)
|
||
|
||
mysql> create table staff_info (s_id int,name varchar(20),dep_id int,foreign key(dep_id) references departments(dep_id));
|
||
ERROR 1215 (HY000): Cannot add foreign key constraint
|
||
|
||
## 当设置字段为unique唯一字段时，设置该字段为外键成功
|
||
mysql> alter table departments modify dep_id int(4) unique;
|
||
Query OK, 0 rows affected (0.01 sec)
|
||
Records: 0 Duplicates: 0 Warnings: 0
|
||
|
||
mysql> desc departments; +----------+-------------+------+-----+---------+-------+
|
||
| Field | Type | Null | Key | Default | Extra |
|
||
+----------+-------------+------+-----+---------+-------+
|
||
| dep_id | int(4) | YES | UNI | NULL | |
|
||
| dep_name | varchar(11) | YES | | NULL | |
|
||
+----------+-------------+------+-----+---------+-------+
|
||
2 rows in set (0.01 sec)
|
||
|
||
mysql> create table staff_info (s_id int,name varchar(20),dep_id int,foreign key(dep_id) references departments(dep_id));
|
||
Query OK, 0 rows affected (0.02 sec)
|
||
```
|
||
```sql
|
||
##表类型必须是innodb存储引擎，且被关联的字段，即references指定的另外一个表的字段，必须保证唯一
|
||
create table department(
|
||
id int primary key,
|
||
name varchar(20) not null
|
||
)engine=innodb;
|
||
|
||
##dpt_id外键，关联父表（department主键id），同步更新，同步删除
|
||
create table employee(
|
||
id int primary key,
|
||
name varchar(20) not null,
|
||
dpt_id int,
|
||
foreign key(dpt_id)
|
||
references department(id)
|
||
on delete cascade # 连级删除
|
||
on update cascade # 连级更新
|
||
)engine=innodb;
|
||
|
||
|
||
##先往父表department中插入记录
|
||
insert into department values
|
||
(1,'教质部'),
|
||
(2,'技术部'),
|
||
(3,'人力资源部');
|
||
|
||
|
||
##再往子表employee中插入记录
|
||
insert into employee values
|
||
(1,'yuan',1),
|
||
(2,'nezha',2),
|
||
(3,'egon',2),
|
||
(4,'alex',2),
|
||
(5,'wusir',3),
|
||
(6,'张三三',3),
|
||
(7,'皮卡丘',3),
|
||
(8,'程咬金',3),
|
||
(9,'程咬银',3)
|
||
;
|
||
|
||
|
||
##删父表department，子表employee中对应的记录跟着删
|
||
mysql> delete from department where id=2;
|
||
Query OK, 1 row affected (0.00 sec)
|
||
|
||
mysql> select * from employee;
|
||
+----+-----------+--------+
|
||
| id | name | dpt_id |
|
||
+----+-----------+--------+
|
||
| 1 | yuan | 1 |
|
||
| 5 | wusir | 3 |
|
||
| 6 | 张三三 | 3 |
|
||
| 7 | 皮卡丘 | 3 |
|
||
| 8 | 程咬金 | 3 |
|
||
| 9 | 程咬银 | 3 |
|
||
+----+-----------+--------+
|
||
6 rows in set (0.00 sec)
|
||
|
||
|
||
##更新父表department，子表employee中对应的记录跟着改
|
||
mysql> update department set id=2 where id=3;
|
||
Query OK, 1 row affected (0.01 sec)
|
||
Rows matched: 1 Changed: 1 Warnings: 0
|
||
|
||
mysql> select * from employee;
|
||
+----+-----------+--------+
|
||
| id | name | dpt_id |
|
||
+----+-----------+--------+
|
||
| 1 | yuan | 1 |
|
||
| 5 | wusir | 2 |
|
||
| 6 | 张三三 | 2 |
|
||
| 7 | 皮卡丘 | 2 |
|
||
| 8 | 程咬金 | 2 |
|
||
| 9 | 程咬银 | 2 |
|
||
+----+-----------+--------+
|
||
6 rows in set (0.00 sec)
|
||
```
|
||
### DCL数据操控语言
|
||
|
||
- DCL是针对权限进行控制
|
||
- 授权
|
||
```sql
|
||
grant all on *.* to root@'192.168.175.%' identified by '123456'
|
||
## 授予root@'192.168.175.%'用户所有权限(非超级管理员)
|
||
grant all on *.* to root@'192.168.175.%' identified by '123456' with grant option;
|
||
## 授权一个超级管路员
|
||
max_queries_per_hour：一个用户每小时可发出的查询数量
|
||
max_updates_per_hour：一个用户每小时可发出的更新数量
|
||
max_connections_per_hour：一个用户每小时可连接到服务器的次数
|
||
max_user_connections：允许同时连接数量
|
||
```
|
||
|
||
- 收回权限
|
||
```sql
|
||
revoke select on *.* from root@'192.168.175.%';
|
||
## 收回select权限
|
||
show grants for root@'192.168.175.%';
|
||
## 查看权限
|
||
```
|
||
### DML数据操作语言
|
||
|
||
- 操作表中的数据
|
||
- 插入数据
|
||
```sql
|
||
insert into stu valus('linux01',1,NOW(),'zhangsan',20,'m',NOW(),110,123456);
|
||
## 基础用法，插入数据
|
||
insert into stu(classid,birth.sname,sage,sgender,comtime,telnum,qq) values('linux01',1,NOW(),'zhangsan',20,'m',NOW(),110,123456);
|
||
## 规范用法，插入数据
|
||
insert into stu(classid,birth.sname,sage,sgender,comtime,telnum,qq) values('linux01',1,NOW(),'zhangsan',20,'m',NOW(),110,123456),
|
||
('linux02',2,NOW(),'zhangsi',21,'f',NOW(),111,1234567);
|
||
## 插入多条数据
|
||
```
|
||
|
||
- 更新数据
|
||
```sql
|
||
update student set sgender='f';
|
||
## 不规范
|
||
update student set sgender='f' where sid=1;
|
||
## 规范update修改
|
||
update student set sgender='f' where 1=1;
|
||
## 如果非要全表修改
|
||
update mysql.user set password=PASSWORD('123456') where user='root' and host='localhost';
|
||
## 修改密码，需要刷新权限flush privileges
|
||
```
|
||
|
||
- 删除数据
|
||
```sql
|
||
delete from student;
|
||
## 不规范
|
||
delete from student where sid=3;
|
||
## 规范删除（危险）
|
||
truncate table student;
|
||
## DDL清空表中的内容
|
||
```
|
||
|
||
- 使用伪删除
|
||
- 有时候一些重要数据不能直接删除，只能伪删除，因为以后还得使用呢
|
||
- 使用update代替delete，将状态改成删除状态，在查询的时候就可以不显示被标记删除的数据
|
||
```sql
|
||
alter table student add status enum(1,0) default 1;
|
||
## 额外添加一个状态列
|
||
update student set status='0' where sid=1;
|
||
## 使用update
|
||
select * from student where status=1;
|
||
## 应用查询存在的数据
|
||
```
|
||
### DQL数据查询语言
|
||
#### 单表查询
|
||
单表查询语法
|
||
```sql
|
||
SELECT 字段1,字段2... FROM 表名
|
||
WHERE 条件
|
||
GROUP BY field
|
||
HAVING 筛选
|
||
ORDER BY field
|
||
LIMIT 限制条数
|
||
```
|
||
关键字执行优先级
|
||
```sql
|
||
from
|
||
where
|
||
group by
|
||
having
|
||
select
|
||
distinct
|
||
order by
|
||
limit
|
||
```
|
||
|
||
1. 找到表:from
|
||
2. 拿着where指定的约束条件，去文件/表中取出一条条记录
|
||
3. 将取出的一条条记录进行分组group by，如果没有group by，则整体作为一组
|
||
4. 将分组的结果进行having过滤
|
||
5. 执行select
|
||
6. 去重
|
||
7. 将结果按条件排序：order by
|
||
8. 限制结果的显示条数
|
||
#### 简单查询
|
||
```sql
|
||
create table employee(
|
||
id int not null unique auto_increment,
|
||
emp_name varchar(20) not null,
|
||
sex enum('male','female') not null default 'male',
|
||
age int(3) unsigned not null default 28,
|
||
hire_date date not null,
|
||
post varchar(50),
|
||
post_comment varchar(100),
|
||
salary double(15,2),
|
||
office int,
|
||
depart_id int
|
||
)engine=innodb default charset=utf8;
|
||
|
||
insert into employee(emp_name,sex,age,hire_date,post,salary,office,depart_id) values
|
||
('草莓','male',18,'20170301','teacher',7300.33,401,1), #以下是教学部
|
||
('蓝莓','male',78,'20150302','teacher',1000000.31,401,1),
|
||
('黑莓','male',81,'20130305','teacher',8300,401,1),
|
||
('桑葚','male',73,'20140701','teacher',3500,401,1),
|
||
('覆盆子','male',28,'20121101','teacher',2100,401,1),
|
||
('葡萄','female',18,'20110211','teacher',9000,401,1),
|
||
('青提','male',18,'19000301','teacher',30000,401,1),
|
||
('红提','male',48,'20101111','teacher',10000,401,1),
|
||
|
||
('蘑菇','female',48,'20150311','sale',3000.13,402,2),#以下是销售部门
|
||
('洋葱','female',38,'20101101','sale',2000.35,402,2),
|
||
('大葱','female',18,'20110312','sale',1000.37,402,2),
|
||
('大蒜','female',18,'20160513','sale',3000.29,402,2),
|
||
('甜椒','female',28,'20170127','sale',4000.33,402,2),
|
||
|
||
('慕斯','male',28,'20160311','operation',10000.13,403,3), #以下是运营部门
|
||
('西米露','male',18,'19970312','operation',20000,403,3),
|
||
('鲜奶吐司','female',18,'20130311','operation',19000,403,3),
|
||
('绿茶布丁','male',18,'20150411','operation',18000,403,3),
|
||
('葡式蛋塔','female',18,'20140512','operation',17000,403,3);
|
||
```
|
||
```sql
|
||
##简单查询
|
||
SELECT id,emp_name,sex,age,hire_date,post,post_comment,salary,office,depart_id
|
||
FROM employee;
|
||
|
||
SELECT * FROM employee;
|
||
|
||
SELECT emp_name,salary FROM employee;
|
||
|
||
##避免重复DISTINCT
|
||
SELECT DISTINCT post FROM employee;
|
||
|
||
##通过四则运算查询
|
||
SELECT emp_name, salary*12 FROM employee;
|
||
SELECT emp_name, salary*12 AS Annual_salary FROM employee;
|
||
SELECT emp_name, salary*12 Annual_salary FROM employee;
|
||
|
||
##定义显示格式
|
||
CONCAT() 函数用于连接字符串
|
||
SELECT CONCAT('姓名: ',emp_name,' 年薪: ', salary*12) AS Annual_salary
|
||
FROM employee;
|
||
|
||
CONCAT_WS() 第一个参数为分隔符
|
||
SELECT CONCAT_WS(':',emp_name,salary*12) AS Annual_salary
|
||
FROM employee;
|
||
|
||
结合CASE语句：
|
||
SELECT
|
||
(
|
||
CASE
|
||
WHEN emp_name = '草莓' THEN
|
||
emp_name
|
||
WHEN emp_name = '蘑菇' THEN
|
||
CONCAT(emp_name,'_BIGSB')
|
||
ELSE
|
||
concat(emp_name, 'SB')
|
||
END
|
||
) as new_name
|
||
FROM
|
||
employee;
|
||
```
|
||
#### where约束
|
||
where字句中可以使用：
|
||
|
||
1. 比较运算符：> < >= <= <> !=
|
||
2. between 80 and 100 值在80到100之间
|
||
3. in(80,90,100) 值是80或90或100
|
||
4. like '123%'
|
||
1. pattern可以是%或_，
|
||
2. %表示任意多字符
|
||
3. _表示一个字符
|
||
5. 逻辑运算符：在多个条件直接可以使用逻辑运算符 and or not
|
||
```sql
|
||
##1:单条件查询
|
||
SELECT emp_name FROM employee
|
||
WHERE post='sale';
|
||
|
||
##2:多条件查询
|
||
SELECT emp_name,salary FROM employee
|
||
WHERE post='teacher' AND salary>10000;
|
||
|
||
##3:关键字BETWEEN AND
|
||
SELECT emp_name,salary FROM employee
|
||
WHERE salary BETWEEN 10000 AND 20000;
|
||
|
||
SELECT emp_name,salary FROM employee
|
||
WHERE salary NOT BETWEEN 10000 AND 20000;
|
||
|
||
##4:关键字IS NULL(判断某个字段是否为NULL不能用等号，需要用IS)
|
||
SELECT emp_name,post_comment FROM employee
|
||
WHERE post_comment IS NULL;
|
||
|
||
SELECT emp_name,post_comment FROM employee
|
||
WHERE post_comment IS NOT NULL;
|
||
|
||
SELECT emp_name,post_comment FROM employee
|
||
WHERE post_comment=''; 注意''是空字符串，不是null
|
||
ps：
|
||
执行
|
||
update employee set post_comment='' where id=2;
|
||
再用上条查看，就会有结果了
|
||
|
||
##5:关键字IN集合查询
|
||
SELECT emp_name,salary FROM employee
|
||
WHERE salary=3000 OR salary=3500 OR salary=4000 OR salary=9000 ;
|
||
|
||
SELECT emp_name,salary FROM employee
|
||
WHERE salary IN (3000,3500,4000,9000) ;
|
||
|
||
SELECT emp_name,salary FROM employee
|
||
WHERE salary NOT IN (3000,3500,4000,9000) ;
|
||
|
||
##6:关键字LIKE模糊查询
|
||
通配符’%’
|
||
SELECT * FROM employee
|
||
WHERE emp_name LIKE 'eg%';
|
||
|
||
通配符’_’
|
||
SELECT * FROM employee
|
||
WHERE emp_name LIKE 'al__';
|
||
```
|
||
小练习
|
||
> 1. 查看岗位是teacher的员工姓名、年龄
|
||
> 2. 查看岗位是teacher且年龄大于30岁的员工姓名、年龄
|
||
> 3. 查看岗位是teacher且薪资在9000-1000范围内的员工姓名、年龄、薪资
|
||
> 4. 查看岗位描述不为NULL的员工信息
|
||
> 5. 查看岗位是teacher且薪资是10000或9000或30000的员工姓名、年龄、薪资
|
||
> 6. 查看岗位是teacher且薪资不是10000或9000或30000的员工姓名、年龄、薪资
|
||
> 7. 查看岗位是teacher且名字是'大'开头的员工姓名、年薪
|
||
|
||
#### group by
|
||
```sql
|
||
单独使用GROUP BY关键字分组
|
||
SELECT post FROM employee GROUP BY post;
|
||
注意：我们按照post字段分组，那么select查询的字段只能是post，想要获取组内的其他相关信息，需要借助函数
|
||
|
||
GROUP BY关键字和GROUP_CONCAT()函数一起使用
|
||
SELECT post,GROUP_CONCAT(emp_name) FROM employee GROUP BY post;#按照岗位分组，并查看组内成员名
|
||
SELECT post,GROUP_CONCAT(emp_name) as emp_members FROM employee GROUP BY post;
|
||
|
||
GROUP BY与聚合函数一起使用
|
||
select post,count(id) as count from employee group by post;#按照岗位分组，并查看每个组有多少人
|
||
```
|
||
**强调：**
|
||
如果我们用unique的字段作为分组的依据，则每一条记录自成一组，这种分组没有意义
|
||
多条记录之间的某个字段值相同，该字段通常用来作为分组的依据
|
||
#### 聚合函数
|
||
```sql
|
||
##强调：聚合函数聚合的是组的内容，若是没有分组，则默认一组
|
||
|
||
示例：
|
||
SELECT COUNT(*) FROM employee;
|
||
SELECT COUNT(*) FROM employee WHERE depart_id=1;
|
||
SELECT MAX(salary) FROM employee;
|
||
SELECT MIN(salary) FROM employee;
|
||
SELECT AVG(salary) FROM employee;
|
||
SELECT SUM(salary) FROM employee;
|
||
SELECT SUM(salary) FROM employee WHERE depart_id=3;
|
||
```
|
||
小练习
|
||
> 1. 查询岗位名以及岗位包含的所有员工名字
|
||
> 2. 查询岗位名以及各岗位内包含的员工个数
|
||
> 3. 查询公司内男员工和女员工的个数
|
||
> 4. 查询岗位名以及各岗位的平均薪资
|
||
> 5. 查询岗位名以及各岗位的最高薪资
|
||
> 6. 查询岗位名以及各岗位的最低薪资
|
||
> 7. 查询男员工与男员工的平均薪资，女员工与女员工的平均薪资
|
||
|
||
#### HAVING过滤
|
||
HAVING与WHERE不一样的地方在于!
|
||
执行优先级从高到低：where > group by > having
|
||
|
||
1. Where 发生在分组group by之前，因而Where中可以有任意字段，但是绝对不能使用聚合函数。
|
||
2. Having发生在分组group by之后，因而Having中可以使用分组的字段，无法直接取到其他字段,可以使用聚合函数
|
||
```sql
|
||
MariaDB [db2]> select * from employee where salary > 100000;
|
||
+----+----------+------+-----+------------+---------+--------------+------------+--------+-----------+
|
||
| id | emp_name | sex | age | hire_date | post | post_comment | salary | office | depart_id |
|
||
+----+----------+------+-----+------------+---------+--------------+------------+--------+-----------+
|
||
| 2 | 蓝莓 | male | 78 | 2015-03-02 | teacher | NULL | 1000000.31 | 401 | 1 |
|
||
+----+----------+------+-----+------------+---------+--------------+------------+--------+-----------+
|
||
1 row in set (0.00 sec)
|
||
|
||
MariaDB [db2]> select post,group_concat(emp_name) from employee group by post having salary > 10000;
|
||
ERROR 1054 (42S22): Unknown column 'salary' in 'having clause'
|
||
MariaDB [db2]> select post,group_concat(emp_name) from employee group by post having avg(salary) > 10000;
|
||
+-----------+------------------------------------------------------------+
|
||
| post | group_concat(emp_name) |
|
||
+-----------+------------------------------------------------------------+
|
||
| operation | 葡式蛋塔,绿茶布丁,鲜奶吐司,西米露,慕斯 |
|
||
| teacher | 红提,青提,葡萄,覆盆子,桑葚,黑莓,蓝莓,草莓 |
|
||
+-----------+------------------------------------------------------------+
|
||
2 rows in set (0.00 sec)
|
||
```
|
||
小练习
|
||
> 1. 查询各岗位内包含的员工个数小于2的岗位名、岗位内包含员工名字、个数
|
||
> 2. 查询各岗位平均薪资大于10000的岗位名、平均工资
|
||
> 3. 查询各岗位平均薪资大于10000且小于20000的岗位名、平均工资
|
||
|
||
#### ORDER BY 查询排序
|
||
```sql
|
||
按单列排序
|
||
SELECT * FROM employee ORDER BY salary;
|
||
SELECT * FROM employee ORDER BY salary ASC;
|
||
SELECT * FROM employee ORDER BY salary DESC;
|
||
|
||
按多列排序:先按照age排序，如果年纪相同，则按照薪资排序
|
||
SELECT * from employee
|
||
ORDER BY age,
|
||
salary DESC;
|
||
```
|
||
小练习
|
||
> 1. 查询所有员工信息，先按照age升序排序，如果age相同则按照hire_date降序排序
|
||
> 2. 查询各岗位平均薪资大于10000的岗位名、平均工资,结果按平均薪资升序排列
|
||
> 3. 查询各岗位平均薪资大于10000的岗位名、平均工资,结果按平均薪资降序排列
|
||
|
||
#### LIMIT 限制查询的记录数
|
||
```sql
|
||
示例：
|
||
SELECT * FROM employee ORDER BY salary DESC
|
||
LIMIT 3; #默认初始位置为0
|
||
|
||
SELECT * FROM employee ORDER BY salary DESC
|
||
LIMIT 0,5; #从第0开始，即先查询出第一条，然后包含这一条在内往后查5条
|
||
|
||
SELECT * FROM employee ORDER BY salary DESC
|
||
LIMIT 5,5; #从第5开始，即先查询出第6条，然后包含这一条在内往后查5条
|
||
```
|
||
#### 使用正则表达式查询
|
||
```sql
|
||
SELECT * FROM employee WHERE emp_name REGEXP '^ale';
|
||
|
||
SELECT * FROM employee WHERE emp_name REGEXP 'on$';
|
||
|
||
SELECT * FROM employee WHERE emp_name REGEXP 'm{2}';
|
||
|
||
|
||
小结：对字符串匹配的方式
|
||
WHERE emp_name = 'egon';
|
||
WHERE emp_name LIKE 'yua%';
|
||
WHERE emp_name REGEXP 'on$';
|
||
```
|
||
#### 多表连接查询
|
||
创建表格
|
||
```sql
|
||
create table department(
|
||
id int,
|
||
name varchar(20)
|
||
)engine=innodb default charset=utf8;
|
||
|
||
create table employee(
|
||
id int primary key auto_increment,
|
||
name varchar(20),
|
||
sex enum('male','female') not null default 'male',
|
||
age int,
|
||
dep_id int
|
||
)engine=innodb default charset=utf8;
|
||
|
||
##插入数据
|
||
insert into department values
|
||
(200,'技术'),
|
||
(201,'人力资源'),
|
||
(202,'销售'),
|
||
(203,'运营');
|
||
|
||
insert into employee(name,sex,age,dep_id) values
|
||
('草莓','male',18,200),
|
||
('蓝莓','female',48,201),
|
||
('黑莓','male',38,201),
|
||
('桑葚','female',28,202),
|
||
('覆盆子','male',18,200),
|
||
('葡萄','female',18,204)
|
||
;
|
||
|
||
mysql> select * from department;
|
||
+------+----------+
|
||
| id | name |
|
||
+------+----------+
|
||
| 200 | 技术 |
|
||
| 201 | 人力资源 |
|
||
| 202 | 销售 |
|
||
| 203 | 运营 |
|
||
+------+----------+
|
||
4 rows in set (0.00 sec)
|
||
|
||
mysql> select * from employee;
|
||
+----+--------+--------+------+--------+
|
||
| id | name | sex | age | dep_id |
|
||
+----+--------+--------+------+--------+
|
||
| 1 | 草莓 | male | 18 | 200 |
|
||
| 2 | 蓝莓 | female | 48 | 201 |
|
||
| 3 | 黑莓 | male | 38 | 201 |
|
||
| 4 | 桑葚 | female | 28 | 202 |
|
||
| 5 | 覆盆子 | male | 18 | 200 |
|
||
| 6 | 葡萄 | female | 18 | 204 |
|
||
+----+--------+--------+------+--------+
|
||
6 rows in set (0.00 sec)
|
||
```
|
||
重点：外链接语法
|
||
```sql
|
||
SELECT 字段列表
|
||
|
||
FROM 表1 INNER|LEFT|RIGHT JOIN 表2
|
||
|
||
ON 表1.字段 = 表2.字段;
|
||
```
|
||
|
||
1. **交叉连接： 不适用任何匹配条件，生成笛卡尔积**
|
||
```sql
|
||
MariaDB [db3]> select * from employee,department;
|
||
+----+-----------+--------+------+--------+------+--------------+
|
||
| id | name | sex | age | dep_id | id | name |
|
||
+----+-----------+--------+------+--------+------+--------------+
|
||
| 1 | 草莓 | male | 18 | 200 | 200 | 技术 |
|
||
| 1 | 草莓 | male | 18 | 200 | 201 | 人力资源 |
|
||
| 1 | 草莓 | male | 18 | 200 | 202 | 销售 |
|
||
| 1 | 草莓 | male | 18 | 200 | 203 | 运营 |
|
||
| 2 | 蓝莓 | female | 48 | 201 | 200 | 技术 |
|
||
| 2 | 蓝莓 | female | 48 | 201 | 201 | 人力资源 |
|
||
| 2 | 蓝莓 | female | 48 | 201 | 202 | 销售 |
|
||
| 2 | 蓝莓 | female | 48 | 201 | 203 | 运营 |
|
||
| 3 | 黑莓 | male | 38 | 201 | 200 | 技术 |
|
||
| 3 | 黑莓 | male | 38 | 201 | 201 | 人力资源 |
|
||
| 3 | 黑莓 | male | 38 | 201 | 202 | 销售 |
|
||
| 3 | 黑莓 | male | 38 | 201 | 203 | 运营 |
|
||
| 4 | 桑葚 | female | 28 | 202 | 200 | 技术 |
|
||
| 4 | 桑葚 | female | 28 | 202 | 201 | 人力资源 |
|
||
| 4 | 桑葚 | female | 28 | 202 | 202 | 销售 |
|
||
| 4 | 桑葚 | female | 28 | 202 | 203 | 运营 |
|
||
| 5 | 覆盆子 | male | 18 | 200 | 200 | 技术 |
|
||
| 5 | 覆盆子 | male | 18 | 200 | 201 | 人力资源 |
|
||
| 5 | 覆盆子 | male | 18 | 200 | 202 | 销售 |
|
||
| 5 | 覆盆子 | male | 18 | 200 | 203 | 运营 |
|
||
| 6 | 葡萄 | female | 18 | 204 | 200 | 技术 |
|
||
| 6 | 葡萄 | female | 18 | 204 | 201 | 人力资源 |
|
||
| 6 | 葡萄 | female | 18 | 204 | 202 | 销售 |
|
||
| 6 | 葡萄 | female | 18 | 204 | 203 | 运营 |
|
||
+----+-----------+--------+------+--------+------+--------------+
|
||
24 rows in set (0.00 sec)
|
||
```
|
||
|
||
2. **内连接： 只连接匹配的行**
|
||
```sql
|
||
##找两张表共有的部分，相当于利用条件从笛卡尔积结果中筛选出了正确的结果
|
||
##department没有204这个部门，因而employee表中关于204这条员工信息没有匹配出来
|
||
mysql> select employee.id,employee.name,employee.age,employee.sex,department.name from employee inner join department on employee.dep_id=department.id;
|
||
+----+-----------+------+--------+--------------+
|
||
| id | name | age | sex | name |
|
||
+----+-----------+------+--------+--------------+
|
||
| 1 | 草莓 | 18 | male | 技术 |
|
||
| 2 | 蓝莓 | 48 | female | 人力资源 |
|
||
| 3 | 黑莓 | 38 | male | 人力资源 |
|
||
| 4 | 桑葚 | 28 | female | 销售 |
|
||
| 5 | 覆盆子 | 18 | male | 技术 |
|
||
+----+-----------+------+--------+--------------+
|
||
5 rows in set (0.01 sec)
|
||
|
||
##上述sql等同于
|
||
mysql> select employee.id,employee.name,employee.age,employee.sex,department.name from employee,department where employee.dep_id=department.id;
|
||
```
|
||
|
||
3. **外连接之左连接： 优先显示左表全部记录**
|
||
|
||
以左表为准，即找出所有员工信息，当然包括没有部门的员工
|
||
本质就是：在内连接的基础上增加左边有右边没有的结果
|
||
```sql
|
||
MariaDB [db3]> select employee.id,employee.name,department.name as depart_name from employee left join department on employee.dep_id=department.id;
|
||
+----+-----------+--------------+
|
||
| id | name | depart_name |
|
||
+----+-----------+--------------+
|
||
| 1 | 草莓 | 技术 |
|
||
| 5 | 覆盆子 | 技术 |
|
||
| 2 | 蓝莓 | 人力资源 |
|
||
| 3 | 黑莓 | 人力资源 |
|
||
| 4 | 桑葚 | 销售 |
|
||
| 6 | 葡萄 | NULL |
|
||
+----+-----------+--------------+
|
||
6 rows in set (0.00 sec)
|
||
```
|
||
|
||
4. **外连接之右连接： 优先显示右表全部记录**
|
||
|
||
以右表为准，即找出所有部门信息，包括没有员工的部门
|
||
本质就是：在内连接的基础上增加右边有左边没有的结果
|
||
```sql
|
||
MariaDB [db3]> select employee.id,employee.name,department.name as depart_name from employee right join department on employee.dep_id=department.id;
|
||
+------+-----------+--------------+
|
||
| id | name | depart_name |
|
||
+------+-----------+--------------+
|
||
| 1 | 草莓 | 技术 |
|
||
| 2 | 蓝莓 | 人力资源 |
|
||
| 3 | 黑莓 | 人力资源 |
|
||
| 4 | 桑葚 | 销售 |
|
||
| 5 | 覆盆子 | 技术 |
|
||
| NULL | NULL | 运营 |
|
||
+------+-----------+--------------+
|
||
6 rows in set (0.00 sec)
|
||
```
|
||
|
||
5. 全外连接： 显示左右两个表全部记录
|
||
|
||
全外连接：在内连接的基础上增加左边有右边没有的和右边有左边没有的结果
|
||
注意：mysql不支持全外连接 full JOIN
|
||
强调：mysql可以使用此种方式间接实现全外连接
|
||
```sql
|
||
mysql> select * from employee left join department on employee.dep_id = department.id union select * from employee right join department on employee.dep_id = department.id;
|
||
+------+--------+--------+------+--------+------+----------+
|
||
| id | name | sex | age | dep_id | id | name |
|
||
+------+--------+--------+------+--------+------+----------+
|
||
| 1 | 草莓 | male | 18 | 200 | 200 | 技术 |
|
||
| 5 | 覆盆子 | male | 18 | 200 | 200 | 技术 |
|
||
| 2 | 蓝莓 | female | 48 | 201 | 201 | 人力资源 |
|
||
| 3 | 黑莓 | male | 38 | 201 | 201 | 人力资源 |
|
||
| 4 | 桑葚 | female | 28 | 202 | 202 | 销售 |
|
||
| 6 | 葡萄 | female | 18 | 204 | NULL | NULL |
|
||
| NULL | NULL | NULL | NULL | NULL | 203 | 运营 |
|
||
+------+--------+--------+------+--------+------+----------+
|
||
7 rows in set (0.00 sec)
|
||
```
|
||
注意 union与union all的区别：union会去掉相同的纪录
|
||
#### 符合条件连接查询
|
||
示例1：以内连接的方式查询employee和department表，并且employee表中的age字段值必须大于25,即找出年龄大于25岁的员工以及员工所在的部门
|
||
```sql
|
||
mysql> select employee.name,department.name from employee inner join department on employee.dep_id = department.id where age > 25;
|
||
+------+----------+
|
||
| name | name |
|
||
+------+----------+
|
||
| 蓝莓 | 人力资源 |
|
||
| 黑莓 | 人力资源 |
|
||
| 桑葚 | 销售 |
|
||
+------+----------+
|
||
3 rows in set (0.00 sec)
|
||
```
|
||
示例2：以内连接的方式查询employee和department表，并且以age字段的升序方式显示
|
||
```sql
|
||
mysql> select employee.id,employee.name,employee.age,department.name from employee,department where employee.dep_id = department.id and age > 25 order by age asc;
|
||
+----+------+------+----------+
|
||
| id | name | age | name |
|
||
+----+------+------+----------+
|
||
| 4 | 桑葚 | 28 | 销售 |
|
||
| 3 | 黑莓 | 38 | 人力资源 |
|
||
| 2 | 蓝莓 | 48 | 人力资源 |
|
||
+----+------+------+----------+
|
||
3 rows in set (0.00 sec)
|
||
```
|
||
#### 子查询
|
||
|
||
1. 子查询是将一个查询语句嵌套在另一个查询语句中。
|
||
2. 内层查询语句的查询结果，可以为外层查询语句提供查询条件。
|
||
3. 子查询中可以包含：IN、NOT IN、ANY、ALL、EXISTS 和 NOT EXISTS等关键字
|
||
4. 还可以包含比较运算符：= 、 !=、> 、<等
|
||
|
||
**带IN关键字的子查询**
|
||
```sql
|
||
select id,name from department
|
||
where id in
|
||
(select dep_id from employee group by dep_id having avg(age) > 25);
|
||
|
||
+------+----------+
|
||
| id | name |
|
||
+------+----------+
|
||
| 201 | 人力资源 |
|
||
| 202 | 销售 |
|
||
+------+----------+
|
||
2 rows in set (0.00 sec)
|
||
```
|
||
**带比较运算符的子查询**
|
||
EXISTS关字键字表示存在。在使用EXISTS关键字时，内层查询语句不返回查询的记录。
|
||
而是返回一个真假值。True或False
|
||
当返回True时，外层查询语句将进行查询；当返回值为False时，外层查询语句不进行查询
|
||
department表中存在dept_id=203，Ture
|
||
```sql
|
||
MariaDB [db3]> select * from employee
|
||
-> where exists
|
||
-> (select id from department where id=200);
|
||
+----+-----------+--------+------+--------+
|
||
| id | name | sex | age | dep_id |
|
||
+----+-----------+--------+------+--------+
|
||
| 1 | 草莓 | male | 18 | 200 |
|
||
| 2 | 蓝莓 | female | 48 | 201 |
|
||
| 3 | 黑莓 | male | 38 | 201 |
|
||
| 4 | 桑葚 | female | 28 | 202 |
|
||
| 5 | 覆盆子 | male | 18 | 200 |
|
||
| 6 | 葡萄 | female | 18 | 204 |
|
||
+----+-----------+--------+------+--------+
|
||
6 rows in set (0.00 sec)
|
||
```
|
||
department表中不存在dept_id=205，False
|
||
```sql
|
||
MariaDB [db3]> select * from employee where exists (select id from department where id=205);
|
||
Empty set (0.01 sec)
|
||
```
|
||
练习：查询每个部门最新入职的那位员工
|
||
```sql
|
||
MariaDB [db4]> SELECT * FROM employee AS t1 INNER JOIN (SELECT post, max(hire_date) max_date FROM employee GROUP BY post ) AS t2 ON t1.post = t2.post WHERE t1.hire_date = t2.max_date;
|
||
+----+--------+--------+-----+------------+-----------+--------------+----------+--------+-----------+-----------+------------+
|
||
| id | name | sex | age | hire_date | post | post_comment | salary | office | depart_id | post | max_date |
|
||
+----+--------+--------+-----+------------+-----------+--------------+----------+--------+-----------+-----------+------------+
|
||
| 1 | 草莓 | male | 18 | 2017-03-01 | teacher | NULL | 7300.33 | 401 | 1 | teacher | 2017-03-01 |
|
||
| 13 | 甜椒 | female | 28 | 2017-01-27 | sale | NULL | 4000.33 | 402 | 2 | sale | 2017-01-27 |
|
||
| 14 | 慕斯 | male | 28 | 2016-03-11 | operation | NULL | 10000.13 | 403 | 3 | operation | 2016-03-11 |
|
||
+----+--------+--------+-----+------------+-----------+--------------+----------+--------+-----------+-----------+------------+
|
||
3 rows in set (0.00 sec)
|
||
```
|