原先值由空变为非空，触发器 update却无动作。各位帮我瞧瞧~

[benly323]

If not exists(Select 1 from deleted) ----Insert
Begin
......
End
If not exists(select 1 from inserted) ---Delete
Begin
......
End
If exists(select 1 from inserted) and exists(select 1 from deleted) ---Update
Begin
......
End

以上是触发器关于 Insert,Delete,Update的定义,但是我当我修改表中信息时，如果内容是空的，Update的触发则无反应。

比如说表A中：
id NAME EMAIL CITY
1 张三 <NULL> 北京
2 李四 [e-mail] 上海
3 王五 [e-mail], 广州

如果我做修改时：
UPDATE student SET EMAIL = '[e-mail]' WHERE (id = 1)
触发器则没做出动作
是否小弟关于修改的定义有问题？ If exists(select 1 from inserted) and exists(select 1 from deleted) ---Update
还望各位请教，谢谢
如果在下说的不明白，或者问的比较小白，请指出，在线等，谢了先~~~

[laowan688]

检查是否更新了某一列，用于 insert 或 update。例：
create trigger f
on tbl
for update
as
if update(status) or update(title)
sql_statement --更新了 status 或 title 列

[-狙击手-]

if update()
...

[wangxuelid]

create table bb 
(id int identity(1,1) primary key, 
 num int ) 

create table aa 
(id int identity(1,1)primary key, 
 num int ) 

insert into aa values(1) 
insert into aa values(2) 
insert into aa values(3) 

insert into bb values(1) 
insert into bb values(2) 
insert into bb values(3) 
select * from  aa 
select * from  bb 


create trigger tr 
on bb 
for delete
as 
if update(num) 
 begin 
  update aa  
    set aa.num=aa.num+inserted.num  
    from aa,inserted 
    where aa.id=inserted.id 
 end 
Else
 Begin
   insert into bb values(113) 
 End


select * from  aa 
select * from  bb 

[bqb]

create trigger t_student on student
after delete,insert,update
as
begin
    delete from A where id in (select id from deleted)

    if not exists (select 1 from A a,inserted i where a.id=i.id)
        insert into A(id,NAME,EMAIL,CITY)
        select id,NAME,EMAIL,CITY from inserted
    else 
        update a set a.EMAIL=i.EMAIL from A a,inserted i where a.id=i.id
end

[benly323]

嗯，谢谢各位，问题解决了，也大受启发，呵呵