MySQL触发器的使用

关键字: MySQL 触发器 1、创建触发器:
语法:

CREATE TRIGGER trigger_name trigger_time trigger_event ON tbl_name   
FOR EACH ROW   
BEGIN   
trigger_stmt   
-
 

END；  

CREATE TRIGGER trigger_name trigger_time trigger_event ON tbl_name
FOR EACH ROW
BEGIN
 trigger_stmt
END；
例子
CREATE TRIGGER SetUserHome after insert ON users   
FOR EACH ROW   
BEGIN   
update `users` set homeLocationX = 128,
homeLocationY=128, homeLocationZ=30
where uuid = NEW.uuid
END 

以上的例子是错误的， 让本表进行触发时进行更新会让程序进入死循环。

系统会报这样的错误：it is already used by statement which invoked this stored function/trigger.

应该改成以下语句：

CREATE TRIGGER SetUserHome before insert ON users   
FOR EACH ROW   
BEGIN   
set New.homeLocationX = 128;
set New.homeLocationY = 128;
set New.homeLocationZ=30;
END 

大写的为关键字
trigger_name:触发器的名字，我常用的命名规则t_name_tableName_(b|a)(i|u|d),t:触发器标识，name:英文名，tableName:表名，b(BEFORE):标识是触发事件之前，a(AFTER):标识触发事件之后,i(insert):标识insert事件，u(update):标识update事件，d(delete):标识delete事件;
trigger_time:触发时间(BEFORE或AFTER)
trigger_event:事件名(insert或update或delete)
tbl_name:表名(必须是永久性表)
trigger_stmt：执行语句(可以是复合语名)，使用别名OLD和NEW，能够引用与触发程序相关的表中的列。
2、删除解发器
语法：
DROP TRIGGER [schema_name.]trigger_name；
注意：以上操作均需SUPER权限
示例：

DROP TRIGGER t_wiley_hotelComment_bu;   
delimiter //   
CREATE TRIGGER t_wiley_hotelComment_bu BEFORE UPDATE ON hotel_comment   
FOR EACH ROW   
BEGIN   
     IF OLD.ispass=0 && NEW.ispass=1 THEN   
        UPDATE hotel_info SET sumcomment=sumcomment+1,sumconsume=sumconsume+NEW.consume,sumservice=sumservice+NEW.service, sumroom=sumroom+NEW.room,sumentiron=sumentiron+NEW.entironment,total=total+(NEW.service+NEW.room+NEW.entironment) WHERE hotel_id=NEW.hotel_id;   
   ELSEIF OLD.ispass=1 && NEW.ispass=0 THEN   
      UPDATE hotel_info SET sumcomment=sumcomment-1,sumconsume=sumconsume-NEW.consume,sumservice=sumservice-NEW.service, sumroom=sumroom-NEW.room,sumentiron=sumentiron-NEW.entironment,total=total-(NEW.service+NEW.room+NEW.entironment) WHERE hotel_id=NEW.hotel_id;   
   END IF;   
END;//   
delimiter ; 

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