求一条语句，请高手指点！TKS！（分有限）
有表Tb,其字段如下：
A B
null ynb01
BY001 ynb01
Bg003 ysp04
Bg004 ysp04
怎么才能选择出B字段内值所对应的A内即有“null”又有与“null”不一样的值？
不知用游标该怎么写？
[解决办法]
select * from Tb where B in (select B from Tb where A is null)
and B in (select B from Tb where A is not null)
[解决办法]
try
Select * From Tb Where B In (Select B From Tb Group By B Having Count(Distinct A) > = 2)
