MySQL触发器(trigger):监视某种情况并触发某种操作
MySQL触发器(trigger):监视某种情况并触发某种操作
一:四要素
触发时间:before/after
地点:table
监视操作:insert/update/delete
触发操作:insert/update/delete
二:创建触发器
delimiter $ #将sql结束符改为$ 方便写触发的sql语句
create trigger triggerName after/before insert/update/delete on tableName
for each row
begin
sql语句; #想要触发的语句
end$
测试表:商品表(g),订单表(o)
三:删除监视器
drop trigger triggerName
四:下定单(o),商品表(g)数据触发更新
create trigger tg after insert on o
for each row
begin
update g set num=num-new.much where id=new.gid;
end$
PS:对于监视操作insert 而言,,新增的行用new 表示
行中的每一列的值,用new.列名 取出
五:删除一个订单,商品表相应增加
create trigger tg after delete on o
for each row
begin
update g set num=num+old.much where id=old.gid;
end$
六:修改一个订单,商品表相应改变
create trigger tg after update on o
for each row
begin
update g set num=num+old.much-new.much where id=old.gid;
end$
七:after与before区别
after 是先完成数据的增删改,再触发,前面的数据操作完成
before是先触发,判断触发的条件是否满足,再对数据进行增删改操作
本文永久更新链接地址:

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