통계/소계 등 통계치취득 ( GROUP BY ROLLUP)

SELECT 
      TO_CHAR(DATE_COL, 'YYYY/MM/DD HH24') AS TIMESLOT
    , COUNT(*) AS CNT 
FROM TBL_SOME
GROUP BY TO_CHAR(DATE_COL, 'YYYY/MM/DD HH24') 
ORDER BY 1;

SELECT 
      TO_CHAR(DATE_COL, 'HH24') AS TIMESLOT
    , COUNT(*) AS CNT 
FROM TBL_SOME
GROUP BY TO_CHAR(DATE_COL, 'HH24') 
ORDER BY 1;

SELECT 
      TO_CHAR(DATE_COL, 'YYYY HH24') AS TIMESLOT
    , COUNT(*) AS CNT
FROM TBL_SOME
GROUP BY TO_CHAR(DATE_COL, 'YYYY HH24')
ORDER BY 1;

SELECT   
      TO_CHAR(DATE_COL, 'YYYY') AS YY
    , TO_CHAR(DATE_COL, 'MM') AS MM
    , TO_CHAR(DATE_COL, 'DD') AS DD
    , TO_CHAR(DATE_COL, 'HH24') AS TM
    , COUNT(*) AS CNT
FROM TBL_SOME
GROUP BY ROLLUP(TO_CHAR(DATE_COL, 'YYYY'),TO_CHAR(DATE_COL, 'MM'),TO_CHAR(DATE_COL, 'DD'),TO_CHAR(DATE_COL, 'HH24'))
ORDER BY 1;