select AGE_NAME,TIME_NAME,count(*) as num
from
(select 
  AGE_NAME,TIME_NAME
from 
  SLEEP_TIME_DTL
INNER JOIN 
  AGE_GRP ON SLEEP_TIME_DTL.AGE_CODE = AGE_GRP.AGE_CODE
INNER JOIN
  SLEEP_TIME ON SLEEP_TIME_DTL.TIME_CODE = SLEEP_TIME.TIME_CODE)

group by AGE_NAME,TIME_NAME;