求一条简单的sql

[yhyhai]

有表X(a1,a2)
a1 a2
----------
01 a
01 b
02 a
02 b
03 a

有表Y(a1,a2)
a1 a2
----------
01 a
01 b
02 a
02 b
03 a
03 b

请问如何通过sql来得到如下结果集?谢谢!
a1 a2
----------
03 b

[shirley_yue]

规则?

[子陌红尘]

select * from Y where not exists(select 1 from X where a1=Y.a1 and a2=Y.a2)

[wzy_love_sly]

哈哈，多给点分

[miaoyuanyan]

应该用到右外部连接

[yhyhai]

to libin_ftsafe
你的sql没有用啊!

[dawugui]

算法?
规则?

没有咋搞?

[wzy_love_sly]

declare @a table (a1 varchar(10),a2 varchar(10))
insert into @a select '01','a'
insert into @a select '01','b'
insert into @a select '02','a'
insert into @a select '02','b'
insert into @a select '03','a'
declare @b table (a1 varchar(10),a2 varchar(10))
insert into @b select '01','a'
insert into @b select '01','b'
insert into @b select '02','a'
insert into @b select '02','b'
insert into @b select '03','a'
insert into @b select '03','b'

select * from @b y where 
not exists(select 1 from @a where a1=Y.a1 and a2=Y.a2)

a1 a2
03 b

怎么会没有用啊!

[yangjiexi]

select * from Y 
where not exists(select 1 from X where X.a1=Y.a1 and X.a2=Y.a2)

[TNT_1st_excellence]

SELECT a1, a2 FROM b
EXCEPT
SELECT a1, a2FROM a

[JL99000]

select * from Y where not exists (select 1 from X where X.a1=Y.a1 and X.a2=Y.a2)

[huzhenqi2008]

select * from Y
where not exists(select * from X,Y where X.a1=Y.a1 and X.a2=Y.a2)

看到红色部分没有?,要联表查询~~~~