Query to Generate aggregate on every 30 mins.

select to_char(first_time, ‘RRRRMMDDHH24’),

COUNT (CASE WHEN TO_NUMBER(TO_CHAR(FIRST_time, ‘MI’)) <= 30 THEN 1 ELSE NULL END) COUNT1,
COUNT (CASE WHEN TO_NUMBER(TO_CHAR(FIRST_time, ‘MI’)) > 30 THEN 1 ELSE NULL END) COUNT2

FROM V$LOG_HISTORY

GROUP BY to_char(first_time, ‘RRRRMMDDHH24’)

order by 1

/

TO_CHAR(FI COUNT1 COUNT2

———- ———- ———-

2010020906 3 1

2010020907 3 1

2010020908 3 1

2010020909 3 1

2010020910 3 1

2010020911 3 1

2010020912 3 1

2010020913 3 1

2010020914 3 1

2010020915 3 1

2010020916 4 2

TO_CHAR(FI COUNT1 COUNT2

———- ———- ———-

2010020917 3 1

2010020918 3 1

2010020919 1 0