오라클 그룹내 중복 데이터 에서 하나의 데이터 뽑아내기

with temp as(  select '1'  idx , '10' dept , '20170703' as lastm ,'기타' as data_etc from dual union all  select '2'  idx , '20' dept , '20170704' as lastm ,'정상' as data_etc from dual union all  select '2'  idx , '20' dept , '20170705' as lastm ,'비정상' as data_etc from dual union all  select '3'  idx , '40' dept , '20170703' as lastm ,'기타' as data_etc from dual union all  select '3'  idx , '40' dept , '20170701' as lastm ,'기타' as data_etc from dual union all  select '4'  idx , '60' dept , '20170703' as lastm ,'기타' as data_etc from dual union all  select '4'  idx , '60' dept , '20170702' as lastm ,'기타' as data_etc from dual  ) select * from (         select a.*              , row_number() over( partition by idx, dept order by lastm desc) rnk         from temp a      )    where rnk = 1 order by idx