1,select查询的基本结构
select 字段
from 表
where 过滤条件
group by 分组条件 having 过滤的第二条件
order by 排序条件
limit 限定结果条件;
2,最简单的查询语句
mysql> select * from user;
+----+----------+----------+---------------------+
| id | username | password | createtime |
+----+----------+----------+---------------------+
| 1 | kenan | kenan | 2012-10-31 15:32:26 |
| 3 | kenan | lele | 2012-10-31 15:32:26 |
+----+----------+----------+---------------------+
3，查询一列或多列
mysql> select username,createtime from user;
+----------+---------------------+
| username | createtime |
+----------+---------------------+
| kenan | 2012-10-31 15:32:26 |
| kenan | 2012-10-31 15:32:26 |
+----------+---------------------+
2 rows in set (0.00 sec)
4,多表查询
mysql> select * from user;
+----+----------+----------+---------------------+
| id | username | password | createtime |
+----+----------+----------+---------------------+
| 1 | kenan | kenan | 2012-10-31 15:32:26 |
| 3 | kenan | lele | 2012-10-31 15:32:26 |
+----+----------+----------+---------------------+
2 rows in set (0.00 sec) mysql> select * from teacher;
+----+------------+---------------------+
| id | username | createtime |
+----+------------+---------------------+
| 1 | Teacher Li | 2012-11-01 21:00:58 |
| 2 | Teacher Le | 2012-11-01 21:02:07 |
+----+------------+---------------------+
2 rows in set (0.00 sec) mysql> select * from user,teacher;
+----+----------+----------+---------------------+----+------------+---------------------+
| id | username | password | createtime | id | username | createtime |
+----+----------+----------+---------------------+----+------------+---------------------+
| 1 | kenan | kenan | 2012-10-31 15:32:26 | 1 | Teacher Li | 2012-11-01 21:00:58 |
| 3 | kenan | lele | 2012-10-31 15:32:26 | 1 | Teacher Li | 2012-11-01 21:00:58 |
| 1 | kenan | kenan | 2012-10-31 15:32:26 | 2 | Teacher Le | 2012-11-01 21:02:07 |
| 3 | kenan | lele | 2012-10-31 15:32:26 | 2 | Teacher Le | 2012-11-01 21:02:07 |
+----+----------+----------+---------------------+----+------------+---------------------+
4 rows in set (0.00 sec) 多表查询中，如果没有限制条件的话，两个表的记录会分别进行匹配,产生的结果就是两个表的笛卡尔积，叫做全连接
下面的这个带有条件的叫做等同连接，相当于在上面的查询结果中挑选出来满足where后面条件的记录，因为没有所有是空的结果。
mysql> select * from user,teacher where user.username = teacher.username;
Empty set (0.00 sec)
5,带有简单的where字句条件查询
mysql> select * from user where id>2;
+----+----------+----------+---------------------+
| id | username | password | createtime |
+----+----------+----------+---------------------+
| 3 | kenan | lele | 2012-10-31 15:32:26 |
+----+----------+----------+---------------------+
1 row in set (0.00 sec)
6,带有in的查询，in用来表示范围
mysql> select * from user where username in ('kenan','Micheal');
+----+----------+----------+---------------------+
| id | username | password | createtime |
+----+----------+----------+---------------------+
| 1 | kenan | kenan | 2012-10-31 15:32:26 |
| 3 | kenan | lele | 2012-10-31 15:32:26 |
+----+----------+----------+---------------------+
2 rows in set (0.00 sec)
这里查询出来username是kenan或者是Micheal的记录
7,between and 用来表示一个字段的范围的查询
mysql> select * from user where id between 2 and 3;
+----+----------+----------+---------------------+
| id | username | password | createtime |
+----+----------+----------+---------------------+
| 3 | kenan | lele | 2012-10-31 15:32:26 |
+----+----------+----------+---------------------+
1 row in set (0.00 sec) mysql> select * from user where id between 3 and 4;
+----+----------+----------+---------------------+
| id | username | password | createtime |
+----+----------+----------+---------------------+
| 3 | kenan | lele | 2012-10-31 15:32:26 |
+----+----------+----------+---------------------+
1 row in set (0.00 sec)
这里分别查询出来id在2和3之间的记录，3到4之间的记录，从结果可以看出 between and是包含边界的，就是>=2而且<=3
8, is null 查询空值
mysql> select * from user ;
+----+----------+----------+---------------------+
| id | username | password | createtime |
+----+----------+----------+---------------------+
| 1 | kenan | kenan | 2012-10-31 15:32:26 |
| 3 | kenan | lele | 2012-10-31 15:32:26 |
| 4 | lele | lele | NULL |
+----+----------+----------+---------------------+
3 rows in set (0.00 sec) mysql> select * from user where createtime is null;
+----+----------+----------+------------+
| id | username | password | createtime |
+----+----------+----------+------------+
| 4 | lele | lele | NULL |
+----+----------+----------+------------+
1 row in set (0.00 sec)
9,用and连接多条件查询 并关系
mysql> select * from user where username = 'kenan' and password = 'kenan';
+----+----------+----------+---------------------+
| id | username | password | createtime |
+----+----------+----------+---------------------+
| 1 | kenan | kenan | 2012-10-31 15:32:26 |
+----+----------+----------+---------------------+
1 row in set (0.00 sec)
10，用or 的多条件查询 这个是或关系，满足一个条件即可
mysql> select * from user where username = 'kenan' or password = 'kenan';
+----+----------+----------+---------------------+
| id | username | password | createtime |
+----+----------+----------+---------------------+
| 1 | kenan | kenan | 2012-10-31 15:32:26 |
| 3 | kenan | lele | 2012-10-31 15:32:26 |
+----+----------+----------+---------------------+
2 rows in set (0.00 sec)
11,聚合函数 count（）用来统计总数
mysql> select count(*) from user;
+----------+
| count(*) |
+----------+
| 3 |
+----------+
1 row in set (0.00 sec)
12，使用sum（）求和，使用avg函数求平均值
mysql> select id from user;
+----+
| id |
+----+
| 1 |
| 3 |
| 4 |
+----+
3 rows in set (0.00 sec) mysql> select sum(id) from user;
+---------+
| sum(id) |
+---------+
| 8 |
+---------+
1 row in set (0.00 sec) mysql> select avg(id) from user;
+---------+
| avg(id) |
+---------+
| 2.6667 |
+---------+
1 row in set (0.04 sec)
13，使用max（）求最大值，使用min求最小值
mysql> select id from user;
+----+
| id |
+----+
| 1 |
| 3 |
| 4 |
+----+
3 rows in set (0.00 sec) mysql> select max(id) from user;
+---------+
| max(id) |
+---------+
| 4 |
+---------+
1 row in set (0.00 sec) mysql> select min(id) from user;
+---------+
| min(id) |
+---------+
| 1 |
+---------+
1 row in set (0.00 sec)
原文链接：http://soukenan.blog.51cto.com/5130995/1047201