触发器问题，高手帮忙

[HawaiiLeo]

if exists(select name from sysobjects where name='AAA' and xtype='U')
drop table AAA
if exists(select name from sysobjects where name='BBB' and xtype='U')
drop table BBB

create table AAA(id int, num int, date datetime)
create table BBB(id int, num int, date datetime)

insert AAA values(1,2,'2001-1-5')
insert BBB values(1,2,'2001-1-5')
go

CREATE TRIGGER dbo.tr_AAA_u ON AAA
for update
as
update BBB
set BBB.num = AAA.num
where BBB.id = deleted.id

错误提示：
(1 row(s) affected)

(1 row(s) affected)

Server: Msg 107, Level 16, State 3, Procedure tr_AAA_u, Line 5
The column prefix 'AAA' does not match with a table name or alias name used in the query.
Server: Msg 107, Level 16, State 1, Procedure tr_AAA_u, Line 5
The column prefix 'deleted' does not match with a table name or alias name used in the query.

[zqllyh]

update BBB
set BBB.num = deleted.num
where BBB.id = deleted.id

[HawaiiLeo]

zqllyh(学习Stupid As Pig中...) ，不好意思，你的答案也不对，错误提示：

Server: Msg 107, Level 16, State 2, Procedure tr_AAA_u, Line 5
The column prefix 'deleted' does not match with a table name or alias name used in the query.
Server: Msg 107, Level 16, State 1, Procedure tr_AAA_u, Line 5
The column prefix 'deleted' does not match with a table name or alias name used in the query.

[caiyunxia]

CREATE TRIGGER dbo.tr_AAA_u ON AAA
for update
as
update BBB
set num = AAA.num
FROM AAA,DELETED
where BBB.id = deleted.id AND AAA.ID=BBB.ID

[HawaiiLeo]

caiyunxia(monkey) 你写的运行成功，能解释一下为什么
update BBB
set BBB.num = AAA.num
where BBB.id = deleted.id

update BBB
set BBB.num = deleted.num
where BBB.id = deleted.id
为什么不对？？