（转载）MySQL笔记之触发器的应用
（转载）http://www.jb51.net/article/36360.htm
触发器是由事件来触发某个操作，这些事件包括INSERT语句，UPDATE语句和DELETE语句。
创建触发器
（1）创建只有一个执行语句的触发器
CREATE TRIGGER 触发器名 BEFORE|AFTER 触发事件 ON 表名 FOR EACH ROW 执行语句
其中，触发器名参数指要创建的触发器的名字
BEFORE和AFTER参数指定了触发执行的时间，在事件之前或是之后
FOR EACH ROW表示任何一条记录上的操作满足触发事件都会触发该触发器
mysql> select * from student; +------+------+ | age | name | +------+------+ | 23 | Rose | | 28 | Mike | +------+------+ 2 rows in set (0.04 sec) mysql> select * from thetime; +---------------------+ | t | +---------------------+ | 2013-04-28 01:05:39 | +---------------------+ 1 row in set (0.00 sec) mysql> create trigger t1 after insert on student for each row -> insert into thetime values(now()); Query OK, 0 rows affected (0.31 sec) mysql> insert into student values(57, 'Jack'); Query OK, 1 row affected (0.10 sec) mysql> select * from thetime; +---------------------+ | t | +---------------------+ | 2013-04-28 01:05:39 | | 2013-04-28 01:11:45 | +---------------------+ 2 rows in set (0.00 sec) mysql>
上面创建了一个名为t1的触发器，一旦在student中有插入动作，就会自动往thetime表里插入当前日期和时间
（2）创建有多个执行语句的触发器
CREATE TRIGGER 触发器名 BEFORE|AFTER 触发事件 ON 表名 FOR EACH ROW BEGIN 执行语句列表 END
其中，BEGIN与END之间的执行语句列表参数表示需要执行的多个语句，不同语句用分号隔开
tips：一般情况下，mysql默认是以 ; 作为结束执行语句，与触发器中需要的分行起冲突
为解决此问题可用DELIMITER，如：DELIMITER ||，可以将结束符号变成||
当触发器创建完成后，可以用DELIMITER ;来将结束符号变成;
mysql> delimiter && mysql> create trigger t2 before delete on student for each row -> begin -> insert into thetime values(now()); -> insert into thetime values(now()); -> end -> && Query OK, 0 rows affected (0.04 sec) mysql> delete from student where age=23 && Query OK, 1 row affected (0.02 sec) mysql> select * from thetime && +---------------------+ | t | +---------------------+ | 2013-04-28 01:05:39 | | 2013-04-28 01:11:45 | | 2013-04-28 01:23:14 | | 2013-04-28 01:23:14 | +---------------------+ 4 rows in set (0.00 sec) mysql> delimiter ;
上面的语句中，开头将结束符号定义为&&，中间定义一个触发器，一旦有满足条件的删除操作
就会执行BEGIN和END中的语句，接着使用&&结束
最后使用DELIMITER ; 将结束符号还原。
查看触发器
（3）show triggers语句查看触发器信息
mysql> show triggers \G *************************** 1. row *************************** Trigger: t1 Event: INSERT Table: student Statement: insert into thetime values(now()) Timing: AFTER Created: NULL sql_mode: Definer: root@localhost character_set_client: utf8 collation_connection: utf8_general_ci Database Collation: latin1_swedish_ci *************************** 2. row *************************** Trigger: t2 Event: DELETE Table: student Statement: begin insert into thetime values(now()); insert into thetime values(now()); end Timing: BEFORE Created: NULL sql_mode: Definer: root@localhost character_set_client: utf8 collation_connection: utf8_general_ci Database Collation: latin1_swedish_ci 2 rows in set (0.01 sec) mysql>
结果会显示所有触发器的基本信息
tips：SHOW TRIGGERS语句无法查询指定的触发器
（4）在tirggers表中查看触发器信息
mysql> select * from information_schema.triggers \G *************************** 1. row *************************** TRIGGER_CATALOG: def TRIGGER_SCHEMA: test TRIGGER_NAME: t1 EVENT_MANIPULATION: INSERT EVENT_OBJECT_CATALOG: def EVENT_OBJECT_SCHEMA: test EVENT_OBJECT_TABLE: student ACTION_ORDER: 0 ACTION_CONDITION: NULL ACTION_STATEMENT: insert into thetime values(now()) ACTION_ORIENTATION: ROW ACTION_TIMING: AFTER ACTION_REFERENCE_OLD_TABLE: NULL ACTION_REFERENCE_NEW_TABLE: NULL ACTION_REFERENCE_OLD_ROW: OLD ACTION_REFERENCE_NEW_ROW: NEW CREATED: NULL SQL_MODE: DEFINER: root@localhost CHARACTER_SET_CLIENT: utf8 COLLATION_CONNECTION: utf8_general_ci DATABASE_COLLATION: latin1_swedish_ci *************************** 2. row *************************** TRIGGER_CATALOG: def TRIGGER_SCHEMA: test TRIGGER_NAME: t2 EVENT_MANIPULATION: DELETE EVENT_OBJECT_CATALOG: def EVENT_OBJECT_SCHEMA: test EVENT_OBJECT_TABLE: student ACTION_ORDER: 0 ACTION_CONDITION: NULL ACTION_STATEMENT: begin insert into thetime values(now()); insert into thetime values(now()); end ACTION_ORIENTATION: ROW ACTION_TIMING: BEFORE ACTION_REFERENCE_OLD_TABLE: NULL ACTION_REFERENCE_NEW_TABLE: NULL ACTION_REFERENCE_OLD_ROW: OLD ACTION_REFERENCE_NEW_ROW: NEW CREATED: NULL SQL_MODE: DEFINER: root@localhost CHARACTER_SET_CLIENT: utf8 COLLATION_CONNECTION: utf8_general_ci DATABASE_COLLATION: latin1_swedish_ci *************************** 3. row *************************** TRIGGER_CATALOG: def TRIGGER_SCHEMA: view TRIGGER_NAME: product_af_insert EVENT_MANIPULATION: INSERT EVENT_OBJECT_CATALOG: def EVENT_OBJECT_SCHEMA: view EVENT_OBJECT_TABLE: product ACTION_ORDER: 0 ACTION_CONDITION: NULL ACTION_STATEMENT: INSERT INTO operate VALUES(null, 'Insert product', now()) ACTION_ORIENTATION: ROW ACTION_TIMING: AFTER ACTION_REFERENCE_OLD_TABLE: NULL ACTION_REFERENCE_NEW_TABLE: NULL ACTION_REFERENCE_OLD_ROW: OLD ACTION_REFERENCE_NEW_ROW: NEW CREATED: NULL SQL_MODE: DEFINER: root@localhost CHARACTER_SET_CLIENT: utf8 COLLATION_CONNECTION: utf8_general_ci DATABASE_COLLATION: latin1_swedish_ci 3 rows in set (0.35 sec) mysql>
结果显示了所有触发器的详细信息，同时，该方法可以查询制定触发器的详细信息
（5）查询指定触发器
mysql> select * from information_schema.triggers where trigger_name='t2' \G *************************** 1. row *************************** TRIGGER_CATALOG: def TRIGGER_SCHEMA: test TRIGGER_NAME: t2 EVENT_MANIPULATION: DELETE EVENT_OBJECT_CATALOG: def EVENT_OBJECT_SCHEMA: test EVENT_OBJECT_TABLE: student ACTION_ORDER: 0 ACTION_CONDITION: NULL ACTION_STATEMENT: begin insert into thetime values(now()); insert into thetime values(now()); end ACTION_ORIENTATION: ROW ACTION_TIMING: BEFORE ACTION_REFERENCE_OLD_TABLE: NULL ACTION_REFERENCE_NEW_TABLE: NULL ACTION_REFERENCE_OLD_ROW: OLD ACTION_REFERENCE_NEW_ROW: NEW CREATED: NULL SQL_MODE: DEFINER: root@localhost CHARACTER_SET_CLIENT: utf8 COLLATION_CONNECTION: utf8_general_ci DATABASE_COLLATION: latin1_swedish_ci 1 row in set (0.04 sec) mysql>
tips：所有触发器信息都存储在information_schema数据库下的triggers表中
可以使用SELECT语句查询，如果触发器信息过多，最好通过TRIGGER_NAME字段指定查询
（6）删除触发器
mysql> drop trigger t1; Query OK, 0 rows affected (0.02 sec) mysql>
删除触发器之后最好使用上面的方法查看一遍
同时，也可以使用database.trig来指定某个数据库中的触发器
tips：如果不需要某个触发器时一定要将这个触发器删除，以免造成意外操作
