SELECT
ID,근무장소,근무월
,DECODE(RN,1,근무수,0) 근무수
,금액
FROM
(
SELECT
테이블.*
,ROW_NUMBER() OVER (PARTITION BY 근무월 ORDER BY 금액 DESC) RN
FROM 테이블
)A
 

참고해보세요~

SELECT id
     , place
     , month
     , CASE WHEN cnt > 1 AND rk = 1
            THEN 0
            ELSE wrkcnt
        END
     , amt
  FROM (
        SELECT id
             , place
             , month
             , amt
             , wrkcnt
             , ROW_NUMBER () OVER ( PARTITION BY id
                                               , month
                                        ORDER BY id
                                               , amt
                                  ) as rk
             , COUNT (*)   OVER ( PARTITION BY id
                                             , month
                                ) as cnt
             
          FROM t#
)

두분다 감사드립니다.