oracle 查詢某一時間段內每個月的最後一天

 SELECT TO_NUMBER(SUBSTR(VC_SGKSRQ, 0, 4)) YEAR,TO_NUMBER(SUBSTR(VC_SGKSRQ, 6, 2)) MONTH,
        MAX(TO_NUMBER(SUBSTR(VC_SGKSRQ, 9, 2))) DAY
   FROM (SELECT SUBSTR(STATSTIME, 1, 10)  VC_SGKSRQ
  FROM YJ_T_XHJDW_DAYSTATS
 WHERE CM_STATIONNUMBER = '46537A2FBB684EB1AB93F84338DCEB08'
   AND DEVICENAME = 'S'
   AND STATSTIME >= '2017-08-01'
   AND STATSTIME <= '2017-11-11'
   AND DWTYPE = 'U')
GROUP BY TO_NUMBER(SUBSTR(VC_SGKSRQ, 0, 4)),TO_NUMBER(SUBSTR(VC_SGKSRQ, 6, 2))
ORDER BY 1,2