[b]什么是触发器？[/b] 触发器是数据库的一个程序，他是用来监听着数据表的某个行为，一旦数据表的这个行为发生了，马上执行相应的sql语句 [b]触发器的语法结构：[/b] create trigger 触发器的名称触发器事件 on 监听的表名 for each row 行为发生后执行的sql语句 触发器事件组成：；两部分组成： 触发器事件发生的时间-----是在监听的表的行为 after before 常用的是after 触发器执行的内容：增删改 创建order 表的时候，需要注意，因为order在mysql中是一个关键字排序，为了避免错误的发生，我们可以添加反引号，表明这不是一个关键字 [b]案例研究：[/b] 一旦生成订单，对应的库存表要减去相应的数据 （1）建两张表 ：一个商品goods表 一个订单order表 mysql> create table goods(goods_id int primary key auto_increment,goods_name var char(64),shop_price decimal(10,2),goods_number int)engine=mysiam default charset =utf8; mysql> create table `order`(goods_id int primary key auto_increment,goods_name v archar(64),buy_number int)engine=mysiam default charset=utf8; mysql> insert into goods values(null,'nokiaN85',2000,35),(null,'iphone4S',4500,3 0),(null,'Lnmia',5000,40),(null,'samsung',4200,20); mysql> select*from goods; +----------+------------+------------+--------------+ | goods_id | goods_name | shop_price | goods_number | +----------+------------+------------+--------------+ | 1 | nokiaN85 | 2000.00 | 35 | | 2 | iphone4S | 4500.00 | 30 | | 3 | Lnmia | 5000.00 | 40 | | 4 | samsung | 4200.00 | 20 | +----------+------------+------------+--------------+ （2）创建触发器 mysql> create trigger alter_goods_number after insert on `order` for each row up date goods set goods_number=goods_number-5 where goods_id=1; mysql> insert into `order` values(1,'nokiaN85',5); mysql> select*from goods; +----------+------------+------------+--------------+ | goods_id | goods_name | shop_price | goods_number | +----------+------------+------------+--------------+ | 1 | nokiaN85 | 2000.00 | 30 | | 2 | iphone4S | 4500.00 | 30 | | 3 | Lnmia | 5000.00 | 40 | | 4 | samsung | 4200.00 | 20 | +----------+------------+------------+--------------+ new 的使用 mysql> create trigger alter_goods_number after insert on `order` for each row up date goods set goods_number=goods_number-new.buy_number where goods_id=new.goods _id; mysql> insert into `order` values(4,'samsung',5); old 的使用 mysql> create trigger back_goods_number after delete on `order` for each row upd ate goods set goods_number=goods_number+old.buy_number where goods_id=old.goods_ id; mysql> delete from `order` where goods_id=1; 更新 (update将之前下的订单撤销，再重新下订单) mysql> create trigger update_goods_number after update on `order` for each row u pdate goods set goods_number=goods_number+old.buy_number-new.buy_number where go ods_id=new.goods_id; mysql> update `order` set buy_number = 10 ;