mysql触发器

触发器，一般不要单独调用，主要发生响应的事件mysql会自动调用。

语法：

create trigger 触发器名称 指定执行的时间 on 指定在什么表上执行操作 影响的行数 需要执行的任务或者业务

mysql> desc data

    -> ;

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

| Field | Type        | Null | Key | Default | Extra |

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

| name  | varchar(20) | YES  |     | NULL    |       |

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

1 row in set (0.01 sec)

mysql> desc chars;

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

| Field | Type    | Null | Key | Default | Extra |

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

| count | int(10) | YES  |     | NULL    |       |

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

1 row in set (0.01 sec)

mysql> insert into chars values(0);

Query OK, 1 row affected (0.05 sec)

mysql> create trigger tr1 after insert on data

    -> for each row update chars set count=count+char_length(new.name);

Query OK, 0 rows affected (0.20 sec)

mysql> select * from chars;

+-------+

| count |

+-------+

|     0 |

+-------+

1 row in set (0.00 sec)

mysql> insert into data values("jack");

Query OK, 1 row affected (0.09 sec)

mysql> select * from chars;

+-------+

| count |

+-------+

|     4 |

+-------+

1 row in set (0.00 sec)

mysql> insert into data values("cainiao");

Query OK, 1 row affected (0.05 sec)

mysql> select * from chars;

+-------+

| count |

+-------+

|    11 |

+-------+

1 row in set (0.00 sec)