2.sql

数据库的开发事例

create trigger upd_order
on 订购单  for  update
as
declare @custom_num  char(8)
if update(客户号)
begin
   if  not exists(select *  from 客户
		  where 客户号=(select  客户号  from  inserted))
   begin
     raiserror('非法客户号！',16,1)
     rollback  transaction
   end
   else
   begin
 	select  @custom_num=客户号  from  inserted
 	if @custom_num is not null
 	begin
	 update  订购单
	 set 订购日期=getdate()
    	 where  订单号=(select  订单号   from  inserted)
 	end
 	
    end
end