洛阳北大青鸟：MySQL触发器的正确创建与删除

洛阳北大青鸟：下面的文章主要描述的是MySQL触发器的正确创建步骤，MySQL触发器的删除，你如果对MySQL触发器的正确创建步骤，MySQL触发器的删除有兴趣的话你就可以点击以下的文章进行观看了。

1、创建MySQL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:MySQL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 sumcommentsumcomment=sumcomment+1,

sumconsumesumconsume=sumconsume+NEW.consume,sumservicesumservice=sumservice+NEW.service,

sumroomsumroom=sumroom+NEW.room,sumentironsumentiron=sumentiron+NEW.entironment,

totaltotal=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 sumcommentsumcomment=sumcomment-1,

sumconsumesumconsume=sumconsume-NEW.consume,sumservicesumservice=sumservice-NEW.service,

sumroomsumroom=sumroom-NEW.room,sumentironsumentiron=sumentiron-NEW.entironment,

totaltotal=total-(NEW.service+NEW.room+NEW.entironment) WHERE hotel_id=NEW.hotel_id;

END IF;

END;//

delimiter ;

以上的相关内容就是对MySQL触发器的使用的介绍，望你能有所收获。