MySQL触发器的创建与删除

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。