MySQL删除命令_DELETE

单表删除语句：

DELETE [LOW_PRIORITY][IGNORE] FROM tbl_name

    [WHERE where_definition]

    [ORDER BY ...]

    [LIMIT row_count]

 

这里只对delete的常用参数及用法做出介绍。

 

说明：

low_priority：强制delete命令被延迟执行，直到没有其它客户端读取本表时再执行。

ignore：使MySQL忽略delete执行所有的错误，而错误会以警告的方式返回。

order by...：表中记录按照指定的顺序进行删除，此子句一般与limit联用才有意义。

limit：指定删除操作的指定行范围。

注意：1）不能把ORDER BY或LIMIT与multiple-table UPDATE（多表更新）同时使用；

           2）当delete伴随有多个限制条件时，是将多个限制条件执行查询操作后，再执行对应的删除操作。

（1）简单单表删除

语句：delete from table_name where [条件]

示例：

mysql> select * from staff;
+----+----------+-------+
| id | name     | slary |
+----+----------+-------+
|   | guoding  |   |
|   | dingtao  |   |
|   | haofugui |  |
|   | guoming  |   |
|   | haotian  |   |
|   | fengfei  |   |
|   | guoting  |   |
|   | guoding  |   |
|   | xiaohua  |   |
+----+----------+-------+
 rows in set (0.00 sec)

mysql> delete from staff where id=9;  //通过where指定要删除的记录或记录组合
Query OK,  row affected (0.00 sec)

mysql> select * from staff;
+----+----------+-------+
| id | name     | slary |
+----+----------+-------+
|   | guoding  |   |
|   | dingtao  |   |
|   | haofugui |  |
|   | guoming  |   |
|   | haotian  |   |
|   | fengfei  |   |
|   | guoting  |   |
|   | guoding  |   |
+----+----------+-------+
 rows in set (0.00 sec)

（2）删除-排序、限制

order by...一般与limit搭配使用才有意义。

如：删除工资最低的记录

mysql> select * from staff;
+----+----------+-------+
| id | name     | slary |
+----+----------+-------+
|   | guoding  |   |
|   | dingtao  |   |
|   | haofugui |  |
|   | guoming  |   |
|   | haotian  |   |
|   | fengfei  |   |
|   | guoting  |   |
|   | guoding  |   |
+----+----------+-------+
 rows in set (0.00 sec)

mysql> delete from staff order by slary asc limit 1; //删除工资最低的数据记录
Query OK,  row affected (0.00 sec)

mysql> select * from staff;
+----+----------+-------+
| id | name     | slary |
+----+----------+-------+
|   | guoding  |   |
|   | dingtao  |   |
|   | haofugui |  |
|   | guoming  |   |
|   | haotian  |   |
|   | fengfei  |   |
|   | guoding  |   |
+----+----------+-------+
 rows in set (0.00 sec)

（3）连接删除

假设有一个post表与staff对应：

mysql> select * from staff;
+----+----------+-------+
| id | name     | slary |
+----+----------+-------+
|   | guoding  |   |
|   | dingtao  |   |
|   | haofugui |  |
|   | guoming  |   |
|   | haotian  |   |
|   | fengfei  |   |
|   | guoding  |   |
+----+----------+-------+
 rows in set (0.00 sec)

mysql> select * from post;
+-----+----------+-------+
| num | name     | level |
+-----+----------+-------+
|   | haotian  |      |
|   | guoming  |      |
|   | haofugui |      |
+-----+----------+-------+
 rows in set (0.00 sec)

现在需要从表staff中删除在post没有对应记录的记录：

mysql> delete staff from staff left join post on staff.name=post.name where post.name is NULL;
Query OK,  rows affected (0.00 sec)

mysql> select * from staff;
+----+----------+-------+
| id | name     | slary |
+----+----------+-------+
|   | haofugui |  |
|   | guoming  |   |
|   | haotian  |   |
+----+----------+-------+
 rows in set (0.00 sec)

在上述删除命令中，也可以引入别名，方便输入，如：

mysql> delete A from staff as A left join post as B on A.name=B.name where B.name is NULL;

注意：NULL不可以用等号（B.name=NULL），正确的应该是B.name is NULL