两列数据，查询其中的重复数据问题

[qingniao8]

表t:

列 A B
1 3
2 7
8 1
a sg
100 100
sg 2

..........

查询结果：显示A数据（不包含B列中与A相同的数据）
结果：
-------------
A
1
2
100
sg
请问这个问题如何写sql?

[liangCK]

select a from tb
intersect
select b from tb

[liangCK]

-------------------------------------
--  Author : liangCK 梁爱兰
--  Comment: 小梁 爱 兰儿
--  Date   : 2009-11-26 15:29:10
-------------------------------------
 
--> 生成测试数据: @tb
DECLARE @tb TABLE (A varchar(3),B varchar(3))
INSERT INTO @tb
SELECT '1','3' UNION ALL
SELECT '2','7' UNION ALL
SELECT '8','1' UNION ALL
SELECT 'a','sg' UNION ALL
SELECT '100','100' UNION ALL
SELECT 'sg','2'

--SQL查询如下:

select A from @tb
intersect
select B from @tb

/*
A
----
1
100
2
sg

(4 行受影响)


*/

[dawugui]

select a from t where a not in (select distinct b from t)

[dawugui]

应该是IN.

select a from t where a in (select distinct b from t)

[icelovey]

-- =============================================
-- Author:      T.O.P
-- Create date: 2009/11/26
-- Version:     SQL SERVER 2005
-- =============================================
declare @TB table([A] varchar(3),[B] varchar(3))
insert @TB
select '1','3' union all
select '2','7' union all
select '8','1' union all
select 'a','sg' union all
select '100','100' union all
select 'sg','2'

select a
from @TB t
where exists(select 1 from @tb where b=t.a)


--测试结果:
/*
a
----
1
2
100
sg

(4 row(s) affected)
*/

[dawugui]

create table t(A varchar(10),B varchar(10)) 
insert into t values('1'  ,      '3') 
insert into t values('2'  ,      '7') 
insert into t values('8'  ,      '1') 
insert into t values('a'  ,      'sg') 
insert into t values('100',      '100') 
insert into t values('sg' ,      '2')
go

select a from t where a in (select distinct b from t) 

drop table t

/*
a          
---------- 
1
2
100
sg

（所影响的行数为 4 行）
*/

[icelovey]

[Quote=引用 1 楼 liangck 的回复:]
select a from tb
intersect
select b from tb
[/Quote]
学习了, intersect

[qingniao8]

噢，晓得了，谢谢！