实用 SQL 语句收藏这篇就够了

1. 创建

1.1 创建数据库

语法：create database db_name

示例：创建应用数据库 awesome_app

1	create database `awesome_app`

1.2 创建表格

语法：create table table_name ( … columns )

示例：创建用户表 users

create table `users`
(
    `id` int,
    `name` char(10),
    `avatar` varchar(300),
    `regtime` date
)

1.3 创建索引

语法：create index index_name on table_name (column_name)

示例：为用户 id 创建索引 idx_id

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create index `idx_id` on `users` (`id`)
/* 创建唯一索引 */
create unique index `idx_id` on `users` (`id`)

1.4 为已存在的列创建主键

更常用的方式是在创建表语句所有列定义的后面添加一行 primary key (column_name)。

语法：alter table users add primary key (column_name)

示例：将用户 id 设为主键

1	alter table users add primary key (`id`)

1.5 为已存在的列创建自增约束

更常用的方式是在创建表语句中添加自增列 id int not null auto_increment。

1	alter table `users` modify `id` int not null auto_increment

2. 插入

语法：

insert into table_name values (value1, value2, …)
insert into table_name (column1, column2, …) values (value1, value2, …)

示例：新增注册用户

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insert into `users` values (1, 'ken', 'http://cdn.awesome_app.com/path/to/xxx/avatar1.jpg', curdate())
/* 指定列插入 */
insert into `users` (`name`, `avatar`) values ('bill', 'http://cdn.awesome_app.com/path/to/xxx/avatar2.jpg')

3. 修改

3.1 修改数据记录

语法：

update table_name set column=new_value where condition
update table_name set column1=new_value1,column2=new_value2,… where condition

示例：

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update `users` set `regtime`=curdate() where `regtime` is null
/* 一次修改多列 */
update `users` set `name`='steven',`avatar`='http://cdn.awesome_app.com/path/to/xxx/steven.jpg' where `id`=1

3.2 修改数据库字符集为 `utf8`

1	alter database `awesome_app` default character set utf8

3.3 修改表字符集为 `utf8`

1	alter table `users` convert to character set utf8

3.4 修改表字段字符集为 `utf8`

1	alter table `users` modify `name` char(10) character set utf8

3.5 修改字段类型

1	alter table `users` modify `regtime` datetime not null

3.5 修改字段默认值

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alter table `users` alter `regtime` set default '2019-10-12 00:00:00'
/* 设置默认为当前时间 current_timestamp，需要重新定义整个列 */
alter table `users` modify `regtime` datetime not null default current_timestamp

3.6 修改字段注释

alter table `users` modify `id` int not null auto_increment comment '用户ID';
alter table `users` modify `name` char(10) comment '用户名';
alter table `users` modify `avatar` varchar(300) comment '用户头像';
alter table `users` modify `regtime` datetime not null default current_timestamp comment '注册时间';

修改后，查看改动后的列：

mysql> show full columns from users;
+---------+--------------+-----------------+------+-----+-------------------+----------------+---------------------------------+--------------+
| Field   | Type         | Collation       | Null | Key | Default           | Extra          | Privileges                      | Comment      |
+---------+--------------+-----------------+------+-----+-------------------+----------------+---------------------------------+--------------+
| id      | int(11)      | NULL            | NO   | PRI | NULL              | auto_increment | select,insert,update,references | 用户ID       |
| name    | char(10)     | utf8_general_ci | YES  |     | NULL              |                | select,insert,update,references | 用户名       |
| avatar  | varchar(300) | utf8_general_ci | YES  |     | NULL              |                | select,insert,update,references | 用户头像     |
| regtime | datetime     | NULL            | NO   |     | CURRENT_TIMESTAMP |                | select,insert,update,references | 注册时间     |
+---------+--------------+-----------------+------+-----+-------------------+----------------+---------------------------------+--------------+

4. 删除

4.1 删除数据记录

语法：delete from table_name where condition

示例：删除用户名未填写的用户

# 先增加一条用户名为空的用户
mysql> insert into `users` (`regtime`) values (curdate());
mysql> select * from users;
+----+--------+----------------------------------------------------+------------+
| id | name   | avatar                                             | regtime    |
+----+--------+----------------------------------------------------+------------+
|  1 | steven | http://cdn.awesome_app.com/path/to/xxx/steven.jpg  | 2019-10-12 |
|  2 | bill   | http://cdn.awesome_app.com/path/to/xxx/avatar2.jpg | 2019-10-12 |
|  3 | NULL   | NULL                                               | 2019-10-12 |
+----+--------+----------------------------------------------------+------------+
# 删除用户名为空的行
mysql> delete from `users` where `name` is null;
mysql> select * from users;
+----+--------+----------------------------------------------------+------------+
| id | name   | avatar                                             | regtime    |
+----+--------+----------------------------------------------------+------------+
|  1 | steven | http://cdn.awesome_app.com/path/to/xxx/steven.jpg  | 2019-10-12 |
|  2 | bill   | http://cdn.awesome_app.com/path/to/xxx/avatar2.jpg | 2019-10-12 |
+----+--------+----------------------------------------------------+------------+

4.2 删除数据库

1	drop database if exists `awesome_app`

4.3 删除表

1	drop table if exists `users`

4.4 清空表中所有数据

这个操作相当于先 drop table 再 create table ，因此需要有 drop 权限。

1	truncate table `users`

4.5 删除索引

1	drop index `idx_id` on `users`

5. 查询

5.1 语法

SELECT
    [ALL | DISTINCT | DISTINCTROW ]
      [HIGH_PRIORITY]
      [STRAIGHT_JOIN]
      [SQL_SMALL_RESULT] [SQL_BIG_RESULT] [SQL_BUFFER_RESULT]
      [SQL_CACHE | SQL_NO_CACHE] [SQL_CALC_FOUND_ROWS]
    select_expr [, select_expr ...]
    [FROM table_references
      [PARTITION partition_list]
    [WHERE where_condition]
    [GROUP BY {col_name | expr | position}
      [ASC | DESC], ... [WITH ROLLUP]]
    [HAVING where_condition]
    [ORDER BY {col_name | expr | position}
      [ASC | DESC], ...]
    [LIMIT {[offset,] row_count | row_count OFFSET offset}]
    [PROCEDURE procedure_name(argument_list)]
    [INTO OUTFILE 'file_name'
        [CHARACTER SET charset_name]
        export_options
      | INTO DUMPFILE 'file_name'
      | INTO var_name [, var_name]]
    [FOR UPDATE | LOCK IN SHARE MODE]]

5.2 单表查询

5.2.1 准备数据：

insert into users (`name`, `avatar`) values
('张三', 'http://cdn.awesome_app.com/path/to/xxx/3.jpg'),
('李四', 'http://cdn.awesome_app.com/path/to/xxx/4.jpg'),
('王五', 'http://cdn.awesome_app.com/path/to/xxx/5.jpg'),
('马六', 'http://cdn.awesome_app.com/path/to/xxx/6.jpg'),
('肖七', 'http://cdn.awesome_app.com/path/to/xxx/7.jpg'),
('刘八', 'http://cdn.awesome_app.com/path/to/xxx/8.jpg'),
('杨九', 'http://cdn.awesome_app.com/path/to/xxx/9.jpg'),
('郑十', 'http://cdn.awesome_app.com/path/to/xxx/10.jpg');

/* 增加重复行 */
insert into users (`name`, `avatar`) values
('张三', 'http://cdn.awesome_app.com/path/to/xxx/3.jpg'),
('李四', 'http://cdn.awesome_app.com/path/to/xxx/4.jpg'),
('王五', 'http://cdn.awesome_app.com/path/to/xxx/5.jpg');

5.2.2 查询所有列

mysql> select * from users;
+----+--------+----------------------------------------------------+---------------------+
| id | name   | avatar                                             | regtime             |
+----+--------+----------------------------------------------------+---------------------+
|  1 | steven | http://cdn.awesome_app.com/path/to/xxx/steven.jpg  | 2019-10-12 00:00:00 |
|  2 | bill   | http://cdn.awesome_app.com/path/to/xxx/avatar2.jpg | 2019-10-12 00:00:00 |
|  3 | 张三   | http://cdn.awesome_app.com/path/to/xxx/3.jpg       | 2019-10-13 10:58:37 |
|  4 | 李四   | http://cdn.awesome_app.com/path/to/xxx/4.jpg       | 2019-10-13 10:58:37 |
|  5 | 王五   | http://cdn.awesome_app.com/path/to/xxx/5.jpg       | 2019-10-13 10:58:37 |
|  6 | 马六   | http://cdn.awesome_app.com/path/to/xxx/6.jpg       | 2019-10-13 10:58:37 |
|  7 | 肖七   | http://cdn.awesome_app.com/path/to/xxx/7.jpg       | 2019-10-13 10:58:37 |
|  8 | 刘八   | http://cdn.awesome_app.com/path/to/xxx/8.jpg       | 2019-10-13 10:58:37 |
|  9 | 杨九   | http://cdn.awesome_app.com/path/to/xxx/9.jpg       | 2019-10-13 10:58:37 |
| 10 | 郑十   | http://cdn.awesome_app.com/path/to/xxx/10.jpg      | 2019-10-13 10:58:37 |
| 11 | 张三   | http://cdn.awesome_app.com/path/to/xxx/3.jpg       | 2019-10-13 11:20:17 |
| 12 | 李四   | http://cdn.awesome_app.com/path/to/xxx/4.jpg       | 2019-10-13 11:20:17 |
| 13 | 王五   | http://cdn.awesome_app.com/path/to/xxx/5.jpg       | 2019-10-13 11:20:17 |
+----+--------+----------------------------------------------------+---------------------+

5.2.3 查询指定列

mysql> select id,name from users;
+----+--------+
| id | name   |
+----+--------+
|  1 | steven |
|  2 | bill   |
|  3 | 张三   |
|  4 | 李四   |
|  5 | 王五   |
|  6 | 马六   |
|  7 | 肖七   |
|  8 | 刘八   |
|  9 | 杨九   |
| 10 | 郑十   |
| 11 | 张三   |
| 12 | 李四   |
| 13 | 王五   |
+----+--------+

5.2.4 查询不重复记录

mysql> select distinct name,avatar  from users;
+--------+----------------------------------------------------+
| name   | avatar                                             |
+--------+----------------------------------------------------+
| steven | http://cdn.awesome_app.com/path/to/xxx/steven.jpg  |
| bill   | http://cdn.awesome_app.com/path/to/xxx/avatar2.jpg |
| 张三   | http://cdn.awesome_app.com/path/to/xxx/3.jpg       |
| 李四   | http://cdn.awesome_app.com/path/to/xxx/4.jpg       |
| 王五   | http://cdn.awesome_app.com/path/to/xxx/5.jpg       |
| 马六   | http://cdn.awesome_app.com/path/to/xxx/6.jpg       |
| 肖七   | http://cdn.awesome_app.com/path/to/xxx/7.jpg       |
| 刘八   | http://cdn.awesome_app.com/path/to/xxx/8.jpg       |
| 杨九   | http://cdn.awesome_app.com/path/to/xxx/9.jpg       |
| 郑十   | http://cdn.awesome_app.com/path/to/xxx/10.jpg      |
+--------+----------------------------------------------------+

5.2.5 限制查询行数

查询前几行

mysql> select id,name from users limit 2;
+----+--------+
| id | name   |
+----+--------+
|  1 | steven |
|  2 | bill   |
+----+--------+

查询从指定偏移(第一行为偏移为0)开始的几行

mysql> select id,name from users limit 2,3;
+----+--------+
| id | name   |
+----+--------+
|  3 | 张三   |
|  4 | 李四   |
|  5 | 王五   |
+----+--------+

5.2.6 排序

# 正序
mysql> select distinct name from users order by name asc limit 3;
+--------+
| name   |
+--------+
| bill   |
| steven |
| 刘八   |
+--------+
# 倒序
mysql> select id,name from users order by id desc limit 3;
+----+--------+
| id | name   |
+----+--------+
| 13 | 王五   |
| 12 | 李四   |
| 11 | 张三   |
+----+--------+

5.2.7 分组

增加城市字段

alter table `users` add `city` varchar(10) comment '用户所在城市' after `name`;
update `users` set `city`='旧金山' where `id`=1;
update `users` set `city`='西雅图' where `id`=2;
update `users` set `city`='北京' where `id` in (3,5,7);
update `users` set `city`='上海' where `id` in (4,6,8);
update `users` set `city`='广州' where `id` between 9 and 10;
update `users` set `city`='深圳' where `id` between 11 and 13;

按城市分组统计用户数

mysql> select city, count(name) as num_of_user from users group by city;
+-----------+-------------+
| city      | num_of_user |
+-----------+-------------+
| 上海      |           3 |
| 北京      |           3 |
| 广州      |           2 |
| 旧金山    |           1 |
| 深圳      |           3 |
| 西雅图    |           1 |
+-----------+-------------+
mysql> select city, count(name) as num_of_user from users group by city having num_of_user=1;
+-----------+-------------+
| city      | num_of_user |
+-----------+-------------+
| 旧金山    |           1 |
| 西雅图    |           1 |
+-----------+-------------+
mysql> select city, count(name) as num_of_user from users group by city having num_of_user>2;
+--------+-------------+
| city   | num_of_user |
+--------+-------------+
| 上海   |           3 |
| 北京   |           3 |
| 深圳   |           3 |
+--------+-------------+

5.3 多表关联查询

5.3.1 准备数据

create table if not exists `orders`
(
    `id` int not null primary key auto_increment comment '订单ID',
    `title` varchar(50) not null comment '订单标题',
    `user_id` int not null comment '用户ID',
    `cretime` timestamp not null default current_timestamp comment '创建时间'
);
create table if not exists `groups`
(
    `id` int not null primary key auto_increment comment '用户组ID',
    `title` varchar(50) not null comment '用户组标题',
    `cretime` timestamp not null default current_timestamp comment '创建时间'
);
alter table `users` add `group_id` int comment '用户分组' after `city`;

insert into `groups` (`title`) values ('大佬'), ('萌新'), ('菜鸡');
insert into `orders` (`title`, `user_id`) values ('《大佬是怎样炼成的？》', 3), ('《MySQL 从萌新到删库跑路》', 6), ('《菜鸡踩坑记》', 9);
update `users` set `group_id`=1 where `id` between 1 and 2;
update `users` set `group_id`=2 where `id` in (4, 6, 8, 10, 12);
update `users` set `group_id`=3 where `id` in (3, 5, 13);

5.3.2 join

join

用于在多个表中查询相互匹配的数据。

mysql> select `users`.`name` as `user_name`, `orders`.`title` as `order_title` from `users`, `orders` where `orders`.`user_id`=`users`.`id`;
+-----------+--------------------------------------+
| user_name | order_title                          |
+-----------+--------------------------------------+
| 张三      | 《大佬是怎样炼成的？》               |
| 马六      | 《MySQL 从萌新到删库跑路》           |
| 杨九      | 《菜鸡踩坑记》                       |
+-----------+--------------------------------------+

inner join

内部连接。效果与 join 一样 , 但用法不同，join 使用 where ，inner join 使用 on 。

mysql> select `users`.`name` as `user_name`, `orders`.`title` as `order_title` from `users` inner join `orders` on `orders`.`user_id`=`users`.`id`;
+-----------+--------------------------------------+
| user_name | order_title                          |
+-----------+--------------------------------------+
| 张三      | 《大佬是怎样炼成的？》               |
| 马六      | 《MySQL 从萌新到删库跑路》           |
| 杨九      | 《菜鸡踩坑记》                       |
+-----------+--------------------------------------+

left join

左连接。返回左表所有行，即使右表中没有匹配的行，不匹配的用 NULL 填充。

mysql> select `users`.`name` as `user_name`, `orders`.`title` as `order_title` from `users` left join `orders` on `orders`.`user_id`=`users`.`id`;
+-----------+--------------------------------------+
| user_name | order_title                          |
+-----------+--------------------------------------+
| 张三      | 《大佬是怎样炼成的？》               |
| 马六      | 《MySQL 从萌新到删库跑路》           |
| 杨九      | 《菜鸡踩坑记》                       |
| steven    | NULL                                 |
| bill      | NULL                                 |
| 李四      | NULL                                 |
| 王五      | NULL                                 |
| 肖七      | NULL                                 |
| 刘八      | NULL                                 |
| 郑十      | NULL                                 |
| 张三      | NULL                                 |
| 李四      | NULL                                 |
| 王五      | NULL                                 |
+-----------+--------------------------------------+

right join

右连接。和 left join 正好相反，会返回右表所有行，即使左表中没有匹配的行，不匹配的用 NULL 填充。

mysql> select `groups`.`title` as `group_title`, `users`.`name` as `user_name` from `groups` right join `users` on `users`.`group_id`=`groups`.`id`;
+-------------+-----------+
| group_title | user_name |
+-------------+-----------+
| 大佬        | steven    |
| 大佬        | bill      |
| 萌新        | 李四      |
| 萌新        | 马六      |
| 萌新        | 刘八      |
| 萌新        | 郑十      |
| 萌新        | 李四      |
| 菜鸡        | 张三      |
| 菜鸡        | 王五      |
| 菜鸡        | 王五      |
| NULL        | 肖七      |
| NULL        | 杨九      |
| NULL        | 张三      |
+-------------+-----------+

5.3.3 union

union 用于合并两个或多个查询结果，合并的查询结果必须具有相同数量的列，并且列拥有形似的数据类型，同时列的顺序相同。

mysql> (select `id`, `title` from `groups`) union (select `id`, `title` from `orders`);
+----+--------------------------------------+
| id | title                                |
+----+--------------------------------------+
|  1 | 大佬                                 |
|  2 | 萌新                                 |
|  3 | 菜鸡                                 |
|  1 | 《大佬是怎样炼成的？》               |
|  2 | 《MySQL 从萌新到删库跑路》           |
|  3 | 《菜鸡踩坑记》                       |
+----+--------------------------------------+

6. 函数

6.1 语法

select function(column) from table_name

6.2 合计函数（Aggregate functions）

合计函数的操作面向一系列的值，并返回一个单一的值。通常与 group by 语句一起用。

函数	描述
avg(column)	返回某列的平均值
count(column)	返回某列的行数（不包括 NULL 值）
count(*)	返回被选行数
first(column)	返回在指定的域中第一个记录的值
last(column)	返回在指定的域中最后一个记录的值
max(column)	返回某列的最高值
min(column)	返回某列的最低值
sum(column)	返回某列的总和

6.3 标量函数（Scalar functions）

函数	描述
ucase(c)	转换为大写
lcase(c)	转换为小写
mid(c, start[, end])	从文本提取字符
len(c)	返回文本长度
instr(c, char)	返回在文本中指定字符的数值位置
left(c, number_of_char)	返回文本的左侧部分
right(c, number_of_char)	返回文本的右侧部分
round(c, decimals)	对数值指定小数位数四舍五入
mod(x, y)	取余（求模）
now()	返回当前的系统日期
format(c, format)	格式化显示
datediff(d, date1, date2)	日期计算

参考

[1] www.w3school.com.cn
[2] dev.mysql.com
[3] sql-syntax-server-administration