一个简单的SQL问题

请问一下如何根据时间来去除相应的重复字段
比如说
  字段：ds_datetime,test1,test2,test3
  2011-05-05 a b dd 
  2011-05-05 a b cc
  2011-05-06 a b ee  
我要得到的数据是这样的
  2011-05 a b dd
  cc
  2011-06 a b ee
在日期相同的情况下 字段test1，test2数据是相同的 请问一下怎么实现

SQL code

select ds_datetime=case when no=1 then ds_datetime else '' end,
       test1=case when no=1 then test1 else '' end,
       test2=case when no=1 then test2 else '' end,test3
from
(select row_number() over(partition by ds_datetime,test1,test2 order by getdate()),
      * 
from tb) t

SQL code

select ds_datetime=case when no=1 then ds_datetime else '' end,
       test1=case when no=1 then test1 else '' end,
       test2=case when no=1 then test2 else '' end,test3
from
(select no=row_number() over(partition by ds_datetime,test1,test2 order by getdate()),
      * 
from tb) t

SQL code

select
   case px when 1 then ds_datetime else '' end as ds_datetime,
   case px when 1 then test1 else '' end as test1,
   case px when 1 then test2 else '' end as test2,
   test3
from
    (select px=row()over(partition by ds_datetime order by getdate()),* from tb)t