SELECT a_id, b, c, count(*) as sumrequests
SELECT a_id, b, c, row_number() over (Partition BY a_id) as row
WHERE row <= 10000
AND a_id in (1, 2, 3)
GROUP BY a_id, b, c;
Try the above code and This will output up to 10,000 randomly-chosen rows per a_id. You can partition it further if you're looking to group by more than just a_id.