use Tempdb
go
--> --> 
 
if not object_id(N'Tempdb..#T') is null
    drop table #T
Go
Create table #T([商品编号] int,[采购日期] Datetime,[采购价] int)
Insert #T
select 10001,'2011-02-03',10 union all
select 10002,'2011-02-03',15 union all
select 10001,'2011-03-05',12 union all
select 10003,'2011-03-05',14 union all
select 10002,'2011-03-14',16 union all
select 10003,'2011-03-14',13
Go
Select * from #T AS a WHERE NOT EXISTS(SELECT 1 FROM #T WHERE [商品编号]=a.[商品编号] AND [采购日期]>a.[采购日期])
/*
商品编号    采购日期    采购价
10001    2011-03-05 00:00:00.000    12
10002    2011-03-14 00:00:00.000    16
10003    2011-03-14 00:00:00.000    13
*/

------解决方案--------------------
探讨

如果同一天同一商品 有N条 但是单价不一样。上面的好像就不适用了。