1 用触发器实现级联删除
 2 问题：创建外键约束，触发器就没用，怎么改触发器
 3 帮帮忙
 4 表1：
 5 --创建帖子表
 6 create table Invitation
 7 (
 8 ID int identity(1,1) not null primary key,
 9 CategoryName varchar(50) not null,
10 InvitationTitle varchar(50) not null,
11 InvitationContent text not null
12 )
13 
14 表2：
15 --创建评论表
16 create table Comment
17 (
18 ID int identity(1,1) not null primary key,
19 InvitationID int not null,
20 CommentContent text not null
21 )
22 
23 
24 --创建外键  
25 alter table Comment
26 add constraint FK_Comment_Invitation
27 foreign key(InvitationID)references Invitation(ID)
28 
29 --触发器
30 --1.删除帖子时候连同其下的评论一起删除
31 create trigger DeleteInvtation on Invitation for delete
32 as
33 declare @ID varchar(50)
34 select @ID=ID from Deleted
35 delete from Comment where InvitationID=@ID