如何删除有主外键关系的数据
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举个例子,比如一个新闻发布系统,有类别表,新闻表和评论表,分别设立主外键关系。
那如何删除类别表中的国际新闻是,连同其下的新闻表和评论表也一同删除呢?
两种方法,第一种很简单,当在创建主外键时,如图所示:
把删除规则设为层叠(SQL2005),在SQL2008中又叫做级联了!
类别表和新闻表,新闻表和评论表都要设为层叠。
第二种就是写触发器了!
这是类别表的触发器:
set ANSI_NULLS ON
set QUOTED_IDENTIFIER ON
go
-- =============================================
-- Author: <zxj>
-- Create date: <2012>
-- Description: <删除类触发器>
-- =============================================
ALTER TRIGGER [trigCategoryDelete]
ON [dbo].[cateGory]
instead of DELETE
AS
BEGIN
--select * from deleted
declare @caid int
select @caid=id from deleted
--delete news where caId=(select id from deleted)
--select * from comment where newsid in(select id from news where caid=@caid)
--删除评论
delete comment where newsID in (select Id from news where caid=@caid)
--删除新闻
delete news where caId=@caid
--删除类别
delete category where id=@caid
END
那如何删除类别表中的国际新闻是,连同其下的新闻表和评论表也一同删除呢?
两种方法,第一种很简单,当在创建主外键时,如图所示:
把删除规则设为层叠(SQL2005),在SQL2008中又叫做级联了!
类别表和新闻表,新闻表和评论表都要设为层叠。
第二种就是写触发器了!
这是类别表的触发器:
set ANSI_NULLS ON
set QUOTED_IDENTIFIER ON
go
-- =============================================
-- Author: <zxj>
-- Create date: <2012>
-- Description: <删除类触发器>
-- =============================================
ALTER TRIGGER [trigCategoryDelete]
ON [dbo].[cateGory]
instead of DELETE
AS
BEGIN
--select * from deleted
declare @caid int
select @caid=id from deleted
--delete news where caId=(select id from deleted)
--select * from comment where newsid in(select id from news where caid=@caid)
--删除评论
delete comment where newsID in (select Id from news where caid=@caid)
--删除新闻
delete news where caId=@caid
--删除类别
delete category where id=@caid
END
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