mysql之DQL查询AS CONCAT LIKE的使用

select 列名1，列名2，... from 表名 [where 条件]

过滤掉重复的列值

select distinct 列名1 from 表名

-- 重复的列值只列出一次(去掉列值重复)

mysql> select distinct(password) from user;

连接concat

select concat(列名1，列名2) from 表名 concat_ws带分隔符

列起别名 as

select 列名1 as 别名，列名2 from 表名

模糊查询

select 列名 ... from 表名 where 列名 like '%字符串%';

mysql> select user_name from user where user_name like '%ng%';

+-----------+

| user_name |

+-----------+

| liming |

| zhangsan |

+-----------+

Mysql之DQL排序以及聚合函数

order by 字段 asc;

order by 字段 desc;

mysql> select user_name,id from user order by id asc;

+-----------+----+

| user_name | id |

+-----------+----+

| liming | 1 |

| zhangsan | 2 |

| 李华 | 3 |

+-----------+----+

3 rows in set (0.01 sec)

mysql> select user_name,id from user order by id desc;

+-----------+----+

| user_name | id |

+-----------+----+

| 李华 | 3 |

| zhangsan | 2 |

| liming | 1 |

+-----------+----+

3 rows in set (0.00 sec)

表中有多少条记录，某列的总和，平均值，最大值，最小值

mysql> select count(*) from user;

mysql> select sum(age) from user;

mysql> select avg(age) from user;

mysql> select max(age) from user;

mysql> select min(age) from user;

分组查询

user表的数据

+----+-----------+-----+----------+----------------+-------------+-------+------+

| id | user_name | sex | password | email | mobile | fee | age |

+----+-----------+-----+----------+----------------+-------------+-------+------+

| 1 | liming | 0 | 123435 | liming@163.com | 13666666666 | 12.21 | 28 |

| 2 | zhangsan | 1 | 229999 | zs@163.com | 13554442907 | 86.21 | 22 |

| 3 | 李华 | 0 | 123435 | lihua@163.com | 1366666666 | 99.12 | 18 |

| 4 | lisi | 1 | 2×××2 | lisi@163.com | 17376756841 | 32.18 | 35 |

| 5 | wangwu | 1 | 888888 | wangwu@163.com | 18511111122 | 38.69 | 26 |

+----+-----------+-----+----------+----------------+-------------+-------+------+

统计sex=1时的人数，sex=0时的人数

mysql> select sex,count(*) from user group by sex;

+-----+----------+

| sex | count(*) |

+-----+----------+

| 0 | 2 |

| 1 | 3 |

+-----+----------+

按照sex进行分组，哪组人数大于2

mysql> select sex from user group by sex having count(*)>2;

+-----+

| sex |

+-----+

| 1 |

+-----+

连接查询

内连接查询

-- where 可换成 on

mysql> select s.id,s.name,m.mark from student as s inner join mark as m where m.stu_id=s.id;

+----+---------+------+

| id | name | mark |

+----+---------+------+

| 2 | xiaoliu | 66 |

| 4 | xiaoli | 77 |

| 5 | xiaopan | 88 |

+----+---------+------+

3 rows in set (0.00 sec)

mysql> select m.id,s.name,m.mark from student as s, mark as m where m.stu_id=s.id;

+----+---------+------+

| id | name | mark |

+----+---------+------+

| 1 | xiaoliu | 66 |

| 2 | xiaoli | 77 |

| 3 | xiaopan | 88 |

+----+---------+------+

3 rows in set (0.00 sec)

外连接查询(左连接查询，右连接查询)

左连接查询

mysql> select s.name,m.mark from student as s left join mark as m on m.stu_id=s.id;

+-----------+------+

| name | mark |

+-----------+------+

| xiaoliu | 66 |

| xiaoli | 77 |

| xiaopan | 88 |

| zhaozhang | NULL |

| xiaowang | NULL |

+-----------+------+

右连接查询

mysql> select s.name,m.mark from student as s right join mark as m on m.stu_id=s.id;

+---------+------+

| name | mark |

+---------+------+

| xiaoliu | 66 |

| xiaoli | 77 |

| xiaopan | 88 |

+---------+------+

联合查询

三种方式实现：查询id=2或id=5的记录

mysql> select * from student where id in(2,5);

mysql> select * from student where id=2 or id=5;

mysql> select * from student where id=2 union all select * from student where id=5;

子查询

mysql> select id from student where id in(select stu_id from mark);

+----+

| id |

+----+

| 2 |

| 4 |

| 5 |

+----+

limit查询

mysql> select * from student limit 2;

+----+-----------+-----+

| id | name | age |

+----+-----------+-----+

| 1 | zhaozhang | 26 |

| 2 | xiaoliu | 27 |

+----+-----------+-----+

mysql> select * from student limit 3,2;

+----+---------+-----+

| id | name | age |

+----+---------+-----+

| 4 | xiaoli | 29 |

| 5 | xiaopan | 30 |

+----+---------+-----+