1.首先新建两张表

 create table tb_goods(  

 id int(11) not null primary key ,

 goods_name varchar(128) not null,

 num int(11) default‘0‘  );

 create table tb_order(  

 orderid int(11) not null primary key,

 goods_id int(11) ,  

 onum int  )

2.触发器语法

create trigger tname

after/before insert/update/delete on tb_goods

for each row //这句是固定的

Begin

 //sql语句  

//对新增的行用NEW表示 对列 用 NEW.列名 来表示

End

3.example:

delimiter $ //遇到$才结束  避免与分号冲突

create trigger tr2

after insert on tb_order

for each row

begin

update tb_goods set num=num-NEW.onum where id = NEW.orderid;

end$

create trigger tr3

after delete on tb_order

for each row

begin  

update tb_goods set num = num + OLD.onum where id = OLD.goods_id ;  //对修改之前的行或者删除的行用OLD表示

end$

 //update tb_goods set num=num+OLD.onum-NEW.onum where id=OLD.orderid

mysql触发器总结