467 lines
9.7 KiB
Markdown
Executable File
467 lines
9.7 KiB
Markdown
Executable File
# MySQL
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[MySQL 教程 | 菜鸟教程](https://www.runoob.com/mysql/mysql-tutorial.html)
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## docker 安装mysql
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1. 创建 docker-compose.yml
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```sh
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vim docker-comopse.yml
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===
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services:
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mysql:
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image: mysql
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restart: on-failure
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environment:
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- MYSQL_ROOT_PASSWORD=Aa123456
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- MYSQL_DATABASE=mybase
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- MYSQL_USER=hxx
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- MYSQL_PASSWORD=Aa123456
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- TZ=Asia/Shanghai
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- character-set-server=utf8mb4
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- collation-server=utf8mb4_unicode_ci
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ports:
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- '3307:3306'
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volumes:
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- ./data:/var/lib/mysql # 数据挂载
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- ./init:/docker-entrypoit-initdb.d/ # 初始脚本
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===
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```
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2. 创建授权 root 用户可以远程链接的脚本
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```sh
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mkdir init
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vim init/remote.sql
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===
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-- GRANT ALL privileges on *.* TO 'root'@'%';
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ALTER USER 'root'@'%' IDENTIFIED WITH mysql_native-pasword BY 'Aa123456';
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===
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```
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* 错误
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Client does not support authentication protocol requested by server; consider upgrading MySQL client
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```sh
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mysql -u root -p
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ALTER USER 'root'@'localhost' IDENTIFIED WITH mysql_native_password BY '你的密码';
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# ALTER USER 'root' IDENTIFIED WITH mysql_native_password BY '你的密码';
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flush privileges;
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# mysq> 加一个闪烁的光标等待命令的输入, 输入 exit 或 quit 退出登录
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```
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## 语法
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* 大小写不敏感
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* 可以单行/多行, 以`;`结束
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* 注释
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* 单行: `-- 注释内容`
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* 单行: `# 注释内容`
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* 多行: `/* 多行内容 */`
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## 数据库操作
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```mysql
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# 查看数据库
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show databases;
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# 使用数据库
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use 数据库名;
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# 创建数据库
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create database 数据库名 [charset utf8];
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# 删除数据库
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drop database 数据库名;
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# 查看当前使用的数据库
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select database();
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```
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## 表操作
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### 查
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```mysql
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# 查看有哪写表, 需要先选择库
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show tables;
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# 查看表的结构
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desc 表名;
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```
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### 增
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```mysql
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# 创建表
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create table 表名称(
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列名称 列类型,
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列名称 列类型,
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......
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);
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/*
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列类型有:
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int 整数
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float 浮点数
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varchar(长度) 文件,长度为数字, 做最大长度限制
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date 日期类型
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timestamp 时间戳
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*/
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# 复制表结构
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create table 新表名 like 旧表名;
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# 复制表
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create table 新表名 as (select * from 旧表名);
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```
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**通用字段**
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* id
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* create_time
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* creator
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* update_time: 默认值可以为 CURRENT_TIMESTAMP
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* update_by
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* remark
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一张表的字段不宜超过20个,超过考虑拆分
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### 删
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```mysql
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# 删除表
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drop table 表名称;
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drop table if exists 表名称;
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```
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### 改
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```mysql
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# 增加字段
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alter table 表名 add 字段名 类型;
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# 删除字段
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alter table 表名 drop 字段名;
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# 更改字段类型
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alter table 表名 modify 字段 类型;
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# 更改字段名
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alter table 表名 change 旧字段 新字段 类型;
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```
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## 增删改查
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### 增
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```mysql
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insert into 表名 [(字段列表)] values (值列表);
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-- 如果为所有字段新增数据, 不需要写字段列表
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-- null 说明由系统自动生成标识列
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-- 如果字段非空, 但有默认值, 可以不赋值
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-- 非空字段, 没有默认值, 一定要赋值
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-- 字符串一定要加引号, 数字可加可不加
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```
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```mysql
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insert into users values (null, '马九', 22, '男', '马家村', 0);
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-- 或者
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insert into users (name, age, address) values ('马十', 21, '马家村');
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# 插入多条
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insert into 表名 [(字段列表)] values (值列表), (值列表), ...;
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```
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### 删
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```mysql
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delete from 表名 where 条件;
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# 清空表
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delete from 表名;
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```
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```mysql
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DELETE from users where name = '马十';
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DELETE from users where id in (1, 3);
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```
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### 改
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```mysql
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updata 表名 set 字段 = 新值, 字段 = 新值 where 条件;
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-- 一定要加上条件, 不加条件所有的都被修改了
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```
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```mysql
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update users set age = 20 where id = 2;
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-- 使用表达式
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update users set age = age + 1 where id = 1;
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```
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```mysql
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UPDATE torrent
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SET url = REPLACE(url, 'mikanani.me', 'mikanime.tv')
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WHERE url LIKE '%mikanani.me%';
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```
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### 查
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```mysql
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-- 注释为双横线加空格
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select 字段 from 表名 [where 条件];
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-- 条件没有可以不写
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-- 返回的结果是虚拟表
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-- 在sql中. 逻辑等和赋值都是用=号
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-- 逻辑与 and
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-- 逻辑或 or
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-- 逻辑非 not
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```
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```mysql
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select * from users;
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select id, name, gender from users;
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select * from users where id = 2;
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select * frm users where id = 2 or id = 3;
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select * from users where gender = '男' and age > 20;
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select * from users where id in (2, 3, 4, 5); -- id在2, 3, 4, 5 范围内
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select * from users where id not in (1, 2); -- id 不包括2, 3, 4, 5
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```
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## 其他常用函数
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### 统计
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```mysql
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-- 统计所有数据条数
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select count(*) from users;
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-- 只统计非空的数据调数, 过滤null
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select count(gender) from users;
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-- 查询最大
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select max(age) from users;
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-- 查询最小
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select min(age) from users;
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-- 求平均, 数值有效
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select avg(age) from users;
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```
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### 排序
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```mysql
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-- asc升序, 默认升序可以不写, desc倒序
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select * from users order by id [asc];
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select * from users order by id desc;
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```
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```mysql
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# 排序
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select 列|聚合函数|* from 表
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[where 条件]
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[group by 列]
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order by 列
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[asc|desc];
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# asc 升序, 默认, 可以不写
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# desc 倒序
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```
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### 分页
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```mysql
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select * from users limit m; -- 前m条
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select * from users limit m, n; -- 查询m+n条记录，去掉前m条，返回后n条记录.m的值越大，查询的性能会越低
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select * from users limit 3 offset 0; -- 从第1条开始, 向下查询3条
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-- offset 偏移
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-- 当m非常大时, 要先查询m+n条记录 , 再取n条, 非常慢, 可以进行优化
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select * from users limit 10000, 100;
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-- 优化思想, 先定位id
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select * from users where id >100001 limit 100;
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```
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```mysql
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# 分页查询
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select 列|聚合函数|* from 表
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[where 条件]
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[group by 列]
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order by 列
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[asc|desc]
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limit n[,m];
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# 只有n, 取n条
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# n, m 跳过n条, 取m条
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```
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### 分组聚合
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```mysql
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# 分组聚合
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select 字段|聚合函数 from 表名 [where 条件] group by 列;
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# group by 出现的哪个列, 只有这个列能用在字段中
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# 按照 group by后面的条件进行分组
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/*
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聚合函数有:
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sum(列) 求和
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avg(列) 平均
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min(列) 最小
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max(列) 最大
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count(列|*) 数量
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*/
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# 按男女分组, 统计平均年龄
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select gender, avg(age) from student group by gender;
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# 数值函数
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# 四舍五入: round()
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# 向上取整: ceil()
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# 向下取整: floor()
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# 按部门求平均工资, 并且过滤出工资大于3000的
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select depnum, ave(salary) as 平均工资 from emp group by depnum having 平均工资>3000;
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# HAVING 子句用于对分组结果进行过滤。它通常与 GROUP BY 子句一起使用，用于筛选聚合函数的结果。
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# WHERE 子句用于在分组前对记录进行过滤
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# as 命名
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```
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**注意事项:**
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* select, from 必写
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* where, group by, order by, limit 按须
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* 执行顺序: from -> where -> group by 和聚合函数 -> select -> order by -> limit
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### 去重
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```mysql
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# 从表中选择不重复的列
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SELECT DISTINCT 字段 FROM 表名;
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# 多列，并且这些列的组合是唯一
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SELECT DISTINCT column1, column2 FROM table_name;
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```
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### 模糊查询
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```mysql
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# like
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# % 表示匹配多个字符
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# _ 表示匹配单个字符
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select * from 表名 where 字段 like '%字符%';
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```
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### 长度
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```mysql
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# 判断字符长度
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select length('一');
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# 获取姓名为两个中文的
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SELECT * FROM users WHERE LENGTH(name)=6;
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```
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### 运算符
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```mysql
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# select 后面 + - * /
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# 应用在数值类型
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# 查询员工半年的工资
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select name, salary*6 as 半年工资 from emp;
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# ifnull(要检查的表达式, 为null时的替代值)
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select name, (salary+ifnull(comm,0))*6 as 半年工资(加奖金) from emp;
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```
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### 日期函数
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```mysql
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select month('2024-01-01');
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select year('2024-01-01');
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select day('2024-01-01');
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select week('2024-01-01');
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select now(); # 当前时间
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# timestampdiff(格式, 开始时间, 结束时间)
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SELECT timestampdiff(DAY, '2024-01-01', NOW());
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```
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### 多表查询
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#### 交叉连接/关联查询
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速度比较慢
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```mysql
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# 交叉连接: cross join
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# 学生表和成绩表关联
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select * from student cross join score where student.Sno=score.Sno;
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# cross join 返回的是笛卡尔积的数据，存在无意义的数据。所以用where过滤掉
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# cross join 简写为逗号
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select * from student, score where student.Sno=score.Sno;
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# 查询每个学生每门课程考多少分
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select student.Sname as 姓名, score.cno as 课程编号, score.Degree as 成绩 from student, score where student.Sno=score.Sno;
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```
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#### 内连接
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```mysql
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# 内连接: 表1 inner join 表2 on 表1.id=表2.id
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# 表1.id于表2.id 描述同一显示事物
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select student.Sname as 姓名, score.cno as 课程编号, score.Degree as 成绩
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from student inner join score
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on student.Sno=score.Sno;
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# 如果三张表: 表1 inner join 表2 on 表1.id=表2.id inner join 表3 on 表2.id=表3.id
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```
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#### 外连接
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```mysql
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# 左外连接: 表1 left join 表2 on 表1.id-表2.id
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-- 返回左表中的所有数据，对应右表不存在的数据，以nul1的形式返回。
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# 右外连接: 表1 right join 表2 on 表1.id-表2.id
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-- 返回右表中的所有数据，对应左表中不存在的数据，以nul1形式返回。
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# 哪些学生没有选修课程的
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select student.Sname as 姓名
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from student left join score on student.sno=score.sno
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where student.degree is NULL;
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```
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#### 子查询
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```mysql
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# 子查询：一个查询语句中，嵌套另一个查询语句。
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-- 多行子查询: in 和 not in
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-- 单行子查询: >, < , >=, <=, !=, 不等于也可以写成<>
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# 哪些学生没有选修课程的
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select * from student where sno not in (select sno from score);
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# 查询成绩表中成绩最高的学生
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select * from student
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where student.sno=score.sno
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and score.degree =
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(select max(degree) from score);
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``` |