sql分组问题

对于两个字段如A,B，怎么样有一条语句实现取出A是有重复的，同时B字段要不相同。

我写了个方法很不好，而且还有个大问题。
select * from tonghang_dianping where dianping in (select dianping from tonghang_dianping group by dianping having count(*)>1) and dianping not in (select dianping from tonghang_dianping group by dianping ,sub_name having count(*)>1)

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SQL code:
select *
from tonghang_dianping K JOIN (SELECT a ,COUNT(*) AS B from tonghang_dianping GROUP BY A ) L
ON K.A=L.A
WHERE b>1

---

修改下

SQL code:
select K.*
from tonghang_dianping K JOIN (SELECT a ,COUNT(*) AS B from tonghang_dianping GROUP BY A ) L
ON K.A=L.A
WHERE l.B>1

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SQL code:
----------------------------------------------------------------
-- Author :fredrickhu(小F，向高手学习)
-- Date :2009-09-23 18:55:16
-- Version:
-- Microsoft SQL Server 2005 - 9.00.4035.00 (Intel X86)
-- Nov 24 2008 13:01:59
-- Copyright (c) 1988-2005 Microsoft Corporation
-- Developer Edition on Windows NT 5.1 (Build 2600: Service Pack 3)
--
-----------------------------------------------------