685 lines
17 KiB
Markdown
685 lines
17 KiB
Markdown
MySQL 备忘清单
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===
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本备忘单旨在快速理解 [MySQL](https://mysql.com) 所涉及的主要概念，提供了最常用的SQL语句，供您参考。
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入门
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---
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### 介绍
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<!--rehype:wrap-class=row-span-3-->
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MySQL 为关系型数据库(Relational Database Management System)，一个关系型数据库由一个或数个表格组成，如下所示的一个表格
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----
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```bash
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name ▼ 键 ▼ 列(col)
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┌┈┈┈┈┬┈┈┈┈┈┈┈┈┬┈┈┈┈┈┈┬┈┈┈┈┈┈┈┐
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┆ id ┆ name ┆ uid ┆ level ┆ ◀ 表头header
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├┈┈┈┈┼┈┈┈┈┈┈┈┈┤┈┈┈┈┈┈┤┈┈┈┈┈┈┈┤
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┆ 1 ┆ mysql ┆ 0 ┆ 3 ┆
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├┈┈┈┈┼┈┈┈┈┈┈┈┈┤┈┈┈┈┈┈┤┈┈┈┈┈┈┈┤
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┆ 2 ┆ redis ┆ 12 ┆ 1 ┆ ◀ 行 row
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└┈┈┈┈┴┈┈┈┈┈┈┈┈┴┈┈┈┈┈┈┴┈┈┈┈┈┈┈┘
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redis ▲ 值
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```
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----
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- `表头(header)` 每一列的名称
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- `列(col)` 具有相同数据类型的数据的集合
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- `行(row)` 每一行用来描述某个人/物的具体信息
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- `值(value)` 行的具体信息，每个值与该列数据类型相同
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- `键(key)` 用来识别某个特定的人/物的方法，有唯一性
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### 登录MySQL
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```shell
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# 默认用户名<root>，-p 是密码，
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# ⚠️参数后面不需要空格
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mysql -h 127.0.0.1 -u <用户名> -p<密码>
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mysql -D 数据库名 -h 主机名 -u 用户名 -p
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mysql -h <host> -P <端口号> -u <user> -p [db_name]
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mysql -h <host> -u <user> -p [db_name]
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```
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### 常用的
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<!--rehype:wrap-class=row-span-3-->
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#### 数据库 Database
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:-|:-
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:-|:-
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`CREATE DATABASE` db `;` | `创建`数据库
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`SHOW DATABASES;` | `列出`数据库
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`USE` db`;` | `切换`到数据库
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`CONNECT` db `;` | `切换`到数据库
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`DROP DATABASE` db`;` | `删除`数据库
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#### 表 Table
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:-|:-
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:-|:-
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`SHOW TABLES;` | 列出当前数据库的表
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`SHOW FIELDS FROM` t`;` | 表的列表字段
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`DESC` t`;` | 显示表格结构
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`SHOW CREATE TABLE`t`;` | 显示创建表sql
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`TRUNCATE TABLE`t`;` | 删除表中的所有数据
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`DROP TABLE`t`;` | 删除表格
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#### Proccess
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:-|:-
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:-|:-
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`show processlist;` | 列出进程
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`kill` pid`;` | 杀死进程
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### 查看 MySQL 信息
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```shell
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# 显示当前mysql的version的各种信息
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mysql> status;
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# 显示当前mysql的version信息
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mysql> select version();
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# 查看 MySQL 端口号
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mysql> show global variables like 'port';
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```
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### 退出MySQL会话
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```bash
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mysql> exit
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```
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退出 `quit;` 或 `\q;` 一样的效果
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### 备份
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创建备份
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```sql
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mysqldump -u user -p db_name > db.sql
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```
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导出不带架构的数据库
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```shell
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mysqldump -u user -p db_name --no-data=true --add-drop-table=false > db.sql
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```
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<!--rehype:className=wrap-text -->
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恢复备份
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```shell
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mysql -u user -p db_name < db.sql
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```
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MySQL 示例
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------
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### 管理表格
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创建一个包含三列的新表
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```sql
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CREATE TABLE t (
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id INT,
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name VARCHAR DEFAULT NOT NULL,
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price INT DEFAULT 0
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PRIMARY KEY(id)
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);
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```
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从数据库中删除表
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```sql
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DROP TABLE t ;
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```
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向表中添加新列
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```sql
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ALTER TABLE t ADD column;
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```
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从表中删除列c
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```sql
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ALTER TABLE t DROP COLUMN c ;
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```
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添加约束
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```sql
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ALTER TABLE t ADD constraint;
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```
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删除约束
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```sql
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ALTER TABLE t DROP constraint;
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```
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将表从t1重命名为t2
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```sql
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ALTER TABLE t1 RENAME TO t2;
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```
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将列 c1 重命名为 c2
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```sql
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ALTER TABLE t1 CHANGE c1 c2 datatype;
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ALTER TABLE table_name RENAME COLUMN c1 TO c2;
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```
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将列c1的数据类型改为datatype
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```sql
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ALTER TABLE t1 MODIFY c1 datatype;
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```
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删除表中的所有数据
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```sql
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TRUNCATE TABLE t;
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```
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### 从表中查询数据
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从表中查询列c1、c2中的数据
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```sql
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SELECT c1, c2 FROM t
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```
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查询表中的所有行和列
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```sql
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SELECT * FROM t
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```
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查询数据并使用条件筛选行
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```sql
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SELECT c1, c2 FROM t
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WHERE condition
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```
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查询表中的不同行
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```sql
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SELECT DISTINCT c1 FROM t
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WHERE condition
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```
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按升序或降序对结果集排序
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```sql
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SELECT c1, c2 FROM t
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ORDER BY c1 ASC [DESC]
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```
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跳过行的偏移并返回下n行
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```sql
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SELECT c1, c2 FROM t
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ORDER BY c1
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LIMIT n OFFSET offset
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```
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使用聚合函数对行进行分组
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```sql
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SELECT c1, aggregate(c2)
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FROM t
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GROUP BY c1
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```
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使用HAVING子句筛选组
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```sql
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SELECT c1, aggregate(c2)
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FROM t
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GROUP BY c1
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HAVING condition
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```
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### 从多个表查询
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<!--rehype:wrap-class=row-span-2-->
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内部连接 t1 和 t2
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```sql
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SELECT c1, c2
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FROM t1
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INNER JOIN t2 ON condition
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```
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左连接t1和t1
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```sql
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SELECT c1, c2
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FROM t1
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LEFT JOIN t2 ON condition
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```
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右连接t1和t2
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```sql
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SELECT c1, c2
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FROM t1
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RIGHT JOIN t2 ON condition
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```
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执行完全外部连接
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```sql
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SELECT c1, c2
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FROM t1
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FULL OUTER JOIN t2 ON condition
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```
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生成表中行的笛卡尔积
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```sql
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SELECT c1, c2
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FROM t1
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CROSS JOIN t2
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```
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执行交叉连接的另一种方法
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```sql
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SELECT c1, c2
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FROM t1, t2
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```
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使用INNER Join子句将t1连接到自身
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```sql
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SELECT c1, c2
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FROM t1 A
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INNER JOIN t1 B ON condition
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```
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使用SQL运算符，合并两个查询中的行
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```sql
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SELECT c1, c2 FROM t1
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UNION [ALL]
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SELECT c1, c2 FROM t2
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```
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返回两个查询的交集
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```sql
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SELECT c1, c2 FROM t1
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INTERSECT
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SELECT c1, c2 FROM t2
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```
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从另一个结果集中减去一个结果集
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```sql
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SELECT c1, c2 FROM t1
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MINUS
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SELECT c1, c2 FROM t2
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```
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使用模式匹配%查询行_
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```sql
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SELECT c1, c2 FROM t1
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WHERE c1 [NOT] LIKE pattern
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```
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查询列表中的行
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```sql
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SELECT c1, c2 FROM t
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WHERE c1 [NOT] IN value_list
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```
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查询两个值之间的行
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```sql
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SELECT c1, c2 FROM t
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WHERE c1 BETWEEN low AND high
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```
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检查表中的值是否为NULL
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```sql
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SELECT c1, c2 FROM t
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WHERE c1 IS [NOT] NULL
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```
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### 使用 SQL 约束
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将c1和c2设置为主键
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```sql
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CREATE TABLE t(
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c1 INT, c2 INT, c3 VARCHAR,
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PRIMARY KEY (c1,c2)
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);
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```
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将c2列设置为外键
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```sql
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CREATE TABLE t1(
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c1 INT PRIMARY KEY,
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c2 INT,
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FOREIGN KEY (c2) REFERENCES t2(c2)
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);
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```
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使c1和c2中的值唯一
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```sql
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CREATE TABLE t(
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c1 INT, c1 INT,
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UNIQUE(c2,c3)
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);
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```
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确保c1>0和c1>=c2中的值
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```sql
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CREATE TABLE t(
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c1 INT, c2 INT,
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CHECK(c1> 0 AND c1 >= c2)
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);
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```
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c2列中的设置值不为NULL
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```sql
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CREATE TABLE t(
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c1 INT PRIMARY KEY,
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c2 VARCHAR NOT NULL
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);
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```
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### 修改数据
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在表格中插入一行
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```sql
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INSERT INTO t(column_list)
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VALUES(value_list);
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```
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在表格中插入多行
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```sql
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INSERT INTO t(column_list)
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VALUES (value_list),
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(value_list), …;
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```
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将行从t2插入t1
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```sql
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INSERT INTO t1(column_list)
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SELECT column_list
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FROM t2;
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```
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更新列c1中所有行的新值
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```sql
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UPDATE t
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SET c1 = new_value;
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```
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更新列c1、c2中与条件匹配的值
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```sql
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UPDATE t
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SET c1 = new_value,
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c2 = new_value
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WHERE condition;
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```
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删除表中的所有数据
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```sql
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DELETE FROM t;
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```
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删除表中的行子集
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```sql
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DELETE FROM t
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WHERE condition;
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```
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### 管理视图
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<!--rehype:wrap-class=row-span-2-->
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创建由c1和c2组成的新视图
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```sql
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CREATE VIEW v(c1,c2)
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AS
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SELECT c1, c2
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FROM t;
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```
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使用选中选项创建新视图
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```sql
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CREATE VIEW v(c1,c2)
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AS
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SELECT c1, c2
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FROM t;
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WITH [CASCADED | LOCAL] CHECK OPTION;
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```
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创建递归视图
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```sql
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CREATE RECURSIVE VIEW v
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AS
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select-statement -- anchor part
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UNION [ALL]
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select-statement; -- recursive part
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```
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创建临时视图
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```sql
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CREATE TEMPORARY VIEW v
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AS
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SELECT c1, c2
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FROM t;
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```
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删除视图
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```sql
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DROP VIEW view_name;
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```
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### 管理触发器
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创建或修改触发器
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```sql
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CREATE OR MODIFY TRIGGER trigger_name
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WHEN EVENT
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ON table_name TRIGGER_TYPE
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EXECUTE stored_procedure;
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```
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#### WHEN
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:-|:-
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:-|:-
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`BEFORE` | 在事件发生前调用
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`AFTER` | 事件发生后调用
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#### EVENT
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:-|:-
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:-|:-
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`INSERT` | 为INSERT调用
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`UPDATE` | 调用UPDATE
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`DELETE` | 调用DELETE
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#### TRIGGER_TYPE
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:-|:-
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:-|:-
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`FOR EACH ROW` | -
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`FOR EACH STATEMENT` | -
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### 管理索引
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在t表的c1和c2上创建索引
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```sql
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CREATE INDEX idx_name
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ON t(c1,c2);
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```
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在t表的c3、c4上创建唯一索引
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```sql
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CREATE UNIQUE INDEX idx_name
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ON t(c3,c4)
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```
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删除索引
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```sql
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DROP INDEX idx_name ON t;
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```
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MySQL 数据类型
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---------
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### Strings
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| - | - |
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|--------------|-----------------------------|
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| `CHAR` | String (0 - 255) |
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| `VARCHAR` | String (0 - 255) |
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| `TINYTEXT` | String (0 - 255) |
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| `TEXT` | String (0 - 65535) |
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| `BLOB` | String (0 - 65535) |
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| `MEDIUMTEXT` | String (0 - 16777215) |
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| `MEDIUMBLOB` | String (0 - 16777215) |
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| `LONGTEXT` | String (0 - 4294967295) |
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| `LONGBLOB` | String (0 - 4294967295) |
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| `ENUM` | One of preset options |
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| `SET` | Selection of preset options |
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### Date & time
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| Data Type | Format |
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|-------------|---------------------|
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| `DATE` | yyyy-MM-dd |
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| `TIME` | hh:mm:ss |
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| `DATETIME` | yyyy-MM-dd hh:mm:ss |
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| `TIMESTAMP` | yyyy-MM-dd hh:mm:ss |
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| `YEAR` | yyyy |
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### Numeric
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| - | - |
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|---------------|---------------------------------------------------------------|
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| `TINYINT x` | Integer (-128 to 127) |
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| `SMALLINT x` | Integer (-32768 to 32767) |
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| `MEDIUMINT x` | Integer (-8388608 to 8388607) |
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| `INT x` | Integer (-2147483648 to 2147483647) |
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| `BIGINT x` | Integer (-9223372036854775808 to 9223372036854775807) |
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| `FLOAT` | Decimal (precise to 23 digits) |
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| `DOUBLE` | Decimal (24 to 53 digits) |
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| `DECIMAL` | "DOUBLE" stored as string |
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## 函数
|
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### 聚合函数
|
||
|
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| 函数 | 解释 |
|
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| :--------- |:-------------------------------|
|
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| `SUM()` | 计算一列值的总和 |
|
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| `AVG()` | 计算一列值的平均值 |
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| `COUNT()` | 计算行数，可选择性地忽略NULL值 |
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| `MAX()` | 找出一列的最大值 |
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| `MIN()` | 找出一列的最小值 |
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### 数学函数
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<!--rehype:wrap-class=col-span-2 -->
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| 函数 | 解释 | 示例语法 | 结果 |
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| :-------------- | :---------------------------------------------- | :----------------------- | :-------- |
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| `ABS(x)` | 返回数值的绝对值 | `ABS(-5)` | 5 |
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| `ROUND(x,y)` | 四舍五入到指定的小数位数，y为小数位数，默认为0 | `ROUND(3.1415,2)` | 3.14 |
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| `FLOOR(x)` | 向下取整至最接近的整数 | `FLOOR(3.7)` | 3 |
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| `CEIL(x)` | 向上取整至最接近的整数 | `CEIL(3.3)` | 4 |
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| `SQRT(x)` | 返回一个数的平方根 | `SQRT(16)` | 4 |
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| `MOD(x,y)` | 返回x除以y的余数 | `MOD(10,3)` | 1 |
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| `RAND([seed])` | 返回0到1之间的随机数，可选种子值 | `RAND()` 或 `RAND(123)` | 0.345... |
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### 日期和时间函数
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| 函数 | 解释 |
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| :--------------- | :-------------------------- |
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| `NOW()` | 返回当前日期和时间 |
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| `CURDATE()` | 返回当前日期 |
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| `CURTIME()` | 返回当前时间 |
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| `DATE_FORMAT()` | 格式化日期时间输出 |
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| `DATEDIFF()` | 计算两个日期之间相差的天数 |
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| `STR_TO_DATE()` | 将字符串转换为日期格式 |
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### 字符串函数
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<!--rehype:wrap-class=col-span-2 -->
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| 函数 | 解释 | 示例语法 | 结果 |
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| :------------------------------ | :------------------------ | ---------------------------- | --------------- |
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| `CONCAT(s1,s2,...)` | 连接两个或更多字符串 | `CONCAT('Hello, ','World!')` | 'Hello, World!' |
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| `LOWER(str)` | 转换为小写 | `LOWER('HELLO')` | 'hello' |
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| `UPPER(str)` | 转换为大写 | `UPPER('world')` | 'WORLD' |
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| `TRIM(str)` | 去除字符串两端空格 | `TRIM(' Hello ')` | 'Hello' |
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| `LEFT(str,len)` | 提取字符串左侧的若干字符 | `LEFT('Hello', 3)` | 'Hel' |
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| `RIGHT(str,len)` | 提取字符串右侧的若干字符 | `RIGHT('Hello', 2)` | 'lo' |
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| `SUBSTR(str,pos,len)` | 提取字符串中的一部分 | `SUBSTR('Hello', 2, 3)` | 'ell' |
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| `REPLACE(str,from_str,to_str)` | 替换字符串中的部分文本 | `REPLACE('Hello', 'l', 'L')` | 'HeLLo' |
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### 高级函数
|
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<!--rehype:wrap-class=col-span-3 -->
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| 函数 | 解释 | 示例语法 | 结果 |
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| ----------------------------------- | -------------------------------------------------- | ------------------------------------------------------------ | ---------------------------------------- |
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| BIN(x) | 返回 x 的二进制编码，x 为十进制数。 | `BIN(2)` | `10` |
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| BINARY(s) | 将字符串 s 转换为二进制字符串。 | `BINARY 'RUNOOB'` | `'RUNOOB'`（显示效果，实际存储为二进制） |
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| CASE | 复合条件函数，根据条件返回不同结果。 | `CASE WHEN 1 > 0 THEN '1 > 0' WHEN 2 > 0 THEN '2 > 0' ELSE '3 > 0' END` | `'1 > 0'` |
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| CAST(x AS type) | 转换数据类型。 | `CAST('2017-08-29' AS DATE)` | `2017-08-29` |
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| COALESCE(expr1, expr2, ..., expr_n) | 返回第一个非空表达式的值。 | `COALESCE(NULL, NULL, 'runoob.com', NULL, 'google.com')` | `'runoob.com'` |
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| CONNECTION_ID() | 返回当前连接的唯一ID。 | `CONNECTION_ID()` | `4292835`（示例值） |
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| CONV(x, f1, f2) | 将 f1 进制数转换为 f2 进制数。 | `CONV(15, 10, 2)` | `1111` |
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| CONVERT(s USING cs) | 转换字符串 s 的字符集为 cs。 | `CHARSET(CONVERT('ABC' USING gbk))` | `gbk` |
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| CURRENT_USER() | 返回当前用户。 | `CURRENT_USER()` | `guest@%` |
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| DATABASE() | 返回当前数据库名。 | `DATABASE()` | `runoob` |
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| IF(expr, v1, v2) | 条件表达式，expr 为真则 v1，否则 v2。 | `IF(1 > 0, '正确', '错误')` | `'正确'` |
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| IFNULL(v1, v2) | 如果 v1 不为 NULL，则返回 v1，否则返回 v2。 | `IFNULL(NULL, 'Hello Word')` | `'Hello Word'` |
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| ISNULL(expression) | 判断表达式是否为 NULL。 | `ISNULL(NULL)` | `1` |
|
||
| LAST_INSERT_ID() | 返回最近生成的 AUTO_INCREMENT 值。 | `LAST_INSERT_ID()` | `6`（示例值） |
|
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| NULLIF(expr1, expr2) | 若 expr1 等于 expr2，则返回 NULL，否则返回 expr1。 | `NULLIF(25, 25)` | `NULL` |
|
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|
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另见
|
||
---
|
||
|
||
- [SQL 基础教程](http://www.w3school.com.cn/sql/index.asp) _(w3school.com.cn)_
|
||
- [SQL 语句教程](http://www.1keydata.com/cn/sql/sql-count.php) _(1keydata.com)_
|
||
- [21分钟 MySQL 基础入门](https://jaywcjlove.github.io/mysql-tutorial/21-minutes-MySQL-basic-entry.html) _(jaywcjlove.github.io)_
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