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: CREATETRIGGERtrigger_nametrigger_timetrigger_eve
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:
<ol class="dp-xml"> <li class="alt"><span><span>CREATE TRIGGER trigger_name trigger_time trigger_event ON tbl_name </span></span></li> <li><span>FOR EACH ROW </span></li> <li class="alt"><span>BEGIN </span></li> <li><span>trigger_stmt </span></li> <li class="alt"><span>END； </span></li> <li><span>CREATE TRIGGER trigger_name trigger_time trigger_event ON tbl_name </span></li> <li class="alt"><span>FOR EACH ROW </span></li> <li><span>BEGIN </span></li> <li class="alt"><span>trigger_stmt </span></li> <li><span>END； </span></li> </ol>
例子
<ol class="dp-xml"> <li class="alt"><span><span>CREATE TRIGGER SetUserHome after insert ON users </span></span></li> <li><span>FOR EACH ROW </span></li> <li class="alt"><span>BEGIN </span></li> <li> <span>update `users` set </span><span class="attribute">homeLocationX</span><span> = </span><span class="attribute-value">128</span><span>, </span> </li> <li class="alt"> <span class="attribute">homeLocationY</span><span>=</span><span class="attribute-value">128</span><span>, </span><span class="attribute">homeLocationZ</span><span>=</span><span class="attribute-value">30</span><span> </span> </li> <li> <span>where </span><span class="attribute">uuid</span><span> = </span><span class="attribute-value">NEW</span><span>.uuid </span> </li> <li class="alt"><span>END </span></li> </ol>
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：
<ol class="dp-xml"> <li class="alt"><span><span>CREATE TRIGGER SetUserHome before insert ON users </span></span></li> <li><span>FOR EACH ROW </span></li> <li class="alt"><span>BEGIN </span></li> <li> <span>set </span><span class="attribute">New.homeLocationX</span><span> = </span><span class="attribute-value">128</span><span>; </span> </li> <li class="alt"> <span>set </span><span class="attribute">New.homeLocationY</span><span> = </span><span class="attribute-value">128</span><span>; </span> </li> <li> <span>set </span><span class="attribute">New.homeLocationZ</span><span>=</span><span class="attribute-value">30</span><span>; </span> </li> <li class="alt"><span>END </span></li> </ol>
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：
<ol class="dp-xml"><li class="alt"><span><span>DROP TRIGGER [schema_name.]trigger_name； </span></span></li></ol>
注意：以上操作均需SUPER权限
示例：
<ol class="dp-xml"> <li class="alt"><span><span>DROP TRIGGER t_wiley_hotelComment_bu; </span></span></li> <li><span>delimiter // </span></li> <li class="alt"><span>CREATE TRIGGER t_wiley_hotelComment_bu BEFORE UPDATE ON hotel_comment </span></li> <li><span>FOR EACH ROW </span></li> <li class="alt"><span>BEGIN </span></li> <li> <span>IF </span><span class="attribute">OLD.ispass</span><span>=</span><span class="attribute-value">0</span><span> && </span><span class="attribute">NEW.ispass</span><span>=</span><span class="attribute-value">1</span><span> THEN </span> </li> <li class="alt"> <span>UPDATE hotel_info SET </span><span class="attribute">sumcomment</span><span class="attribute-value">sumcomment</span><span>=sumcomment+1,<p></p></span><span class="attribute">sumconsume</span><span class="attribute-value">sumconsume</span><span>=sumconsume+NEW.consume,</span><span class="attribute">sumservice</span><span class="attribute-value">sumservice</span><span>=sumservice+NEW.service, <p></p></span><span class="attribute">sumroom</span><span class="attribute-value">sumroom</span><span>=sumroom+NEW.room,</span><span class="attribute">sumentiron</span><span class="attribute-value">sumentiron</span><span>=sumentiron+NEW.entironment,<p></p></span><span class="attribute">total</span><span class="attribute-value">total</span><span>=total+(NEW.service+NEW.room+NEW.entironment) WHERE </span><span class="attribute">hotel_id</span><span>=</span><span class="attribute-value">NEW</span><span>.hotel_id; </span> </li> <li> <span>ELSEIF </span><span class="attribute">OLD.ispass</span><span>=</span><span class="attribute-value">1</span><span> && </span><span class="attribute">NEW.ispass</span><span>=</span><span class="attribute-value">0</span><span> THEN </span> </li> <li class="alt"> <span>UPDATE hotel_info SET </span><span class="attribute">sumcomment</span><span class="attribute-value">sumcomment</span><span>=sumcomment-1,<p></p></span><span class="attribute">sumconsume</span><span class="attribute-value">sumconsume</span><span>=sumconsume-NEW.consume,</span><span class="attribute">sumservice</span><span class="attribute-value">sumservice</span><span>=sumservice-NEW.service, <p></p></span><span class="attribute">sumroom</span><span class="attribute-value">sumroom</span><span>=sumroom-NEW.room,</span><span class="attribute">sumentiron</span><span class="attribute-value">sumentiron</span><span>=sumentiron-NEW.entironment,<p></p></span><span class="attribute">total</span><span class="attribute-value">total</span><span>=total-(NEW.service+NEW.room+NEW.entironment) WHERE </span><span class="attribute">hotel_id</span><span>=</span><span class="attribute-value">NEW</span><span>.hotel_id; </span> </li> <li><span>END IF; </span></li> <li class="alt"><span>END;// </span></li> <li><span>delimiter ; </span></li> </ol>
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。
