oracle 歸檔切換頻率

 SELECT TO_CHAR(first_time, 'MM/DD') DAY,     
 SUM(DECODE(TO_CHAR(first_time, 'HH24'), '00', 1, 0)) H00,   
   SUM(DECODE(TO_CHAR(first_time, 'HH24'), '01', 1, 0)) H01,     
   SUM(DECODE(TO_CHAR(first_time, 'HH24'), '02', 1, 0)) H02,    
    SUM(DECODE(TO_CHAR(first_time, 'HH24'), '03', 1, 0)) H03,   
      SUM(DECODE(TO_CHAR(first_time, 'HH24'), '04', 1, 0)) H04,     
      SUM(DECODE(TO_CHAR(first_time, 'HH24'), '05', 1, 0)) H05,
     SUM(DECODE(TO_CHAR(first_time, 'HH24'), '06', 1, 0)) H06,
     SUM(DECODE(TO_CHAR(first_time, 'HH24'), '07', 1, 0)) H07,
     SUM(DECODE(TO_CHAR(first_time, 'HH24'), '08', 1, 0)) H08,
     SUM(DECODE(TO_CHAR(first_time, 'HH24'), '09', 1, 0)) H09,
     SUM(DECODE(TO_CHAR(first_time, 'HH24'), '10', 1, 0)) H10,
     SUM(DECODE(TO_CHAR(first_time, 'HH24'), '11', 1, 0)) H11,
     SUM(DECODE(TO_CHAR(first_time, 'HH24'), '12', 1, 0)) H12,
     SUM(DECODE(TO_CHAR(first_time, 'HH24'), '13', 1, 0)) H13,
     SUM(DECODE(TO_CHAR(first_time, 'HH24'), '14', 1, 0)) H14,
     SUM(DECODE(TO_CHAR(first_time, 'HH24'), '15', 1, 0)) H15,   
     SUM(DECODE(TO_CHAR(first_time, 'HH24'), '16', 1, 0)) H16,
     SUM(DECODE(TO_CHAR(first_time, 'HH24'), '17', 1, 0)) H17,
     SUM(DECODE(TO_CHAR(first_time, 'HH24'), '18', 1, 0)) H18,
     SUM(DECODE(TO_CHAR(first_time, 'HH24'), '19', 1, 0)) H19,
     SUM(DECODE(TO_CHAR(first_time, 'HH24'), '20', 1, 0)) H20,
     SUM(DECODE(TO_CHAR(first_time, 'HH24'), '21', 1, 0)) H21,
     SUM(DECODE(TO_CHAR(first_time, 'HH24'), '22', 1, 0)) H22,
     SUM(DECODE(TO_CHAR(first_time, 'HH24'), '23', 1, 0)) H23,
     COUNT(*) TOTAL
  FROM (SELECT ROWNUM RN, FIRST_TIME
        FROM V$LOG_HISTORY
       WHERE first_time > sysdate - 18
         and FIRST_TIME > ADD_MONTHS(SYSDATE, -1)
       ORDER BY FIRST_TIME)
  GROUP BY TO_CHAR(first_time, 'MM/DD')
  ORDER BY MIN(RN);