PHP之路——MySql查询语句

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

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