1.sql

数据库的开发事例

create trigger del_order
on 订购单  for  delete
as
declare @order_num  char(8)

begin
   if  not exists(select *  from 订购单
		  where 订单号=(select  订单号  from  deleted))
   begin
     raiserror('非法订购单号！',16,1)
     rollback  transaction
   end
   else
   begin
 	select  @order_num=订单号  from  deleted
 	if   exists (select *  from 订单明细表
		  where 订单号=@order_num)
 	begin
		 --raiserror('不允许删除！',16,1)

    		delete  from 订单明细表 where 订单号=@order_num
		commit transaction
 	end
 	else 
        begin
          commit transaction
	end
    end
end