SELECT TO_CHAR(FIRST_TIME,'YYYY-MM-DD') DAY,
TO_CHAR(FIRST_TIME,'HH24') HOUR,
COUNT(*) TOTAL
FROM V$LOG_HISTORY
GROUP BY TO_CHAR(FIRST_TIME,'YYYY-MM-DD'),TO_CHAR(FIRST_TIME,'HH24')
ORDER BY TO_CHAR(FIRST_TIME,'YYYY-MM-DD'),TO_CHAR(FIRST_TIME,'HH24')
ASC
/