SQL(oracle) 取得分组后最大值记录

select * from 
(select t.*, row_number() over(partition by 分组字段 order by 排序字段 desc ) rn
from tablename t )
where rn=1

select *

  from (select t.*,

               row_number() over(partition by campaignid order by createat desc) rn

          from app_campaigntype_summary t

         where createat <= to_date('2015-01-09', 'yyyy-mm-dd'))

 where rn = 1