QUERY PLAN
Limit (cost=69.47..69.49 rows=10 width=195)
-> Sort (cost=69.47..70.09 rows=248 width=195)
Sort Key: s.created_at DESC
-> HashAggregate (cost=61.63..64.11 rows=248 width=195)
Group Key: s.id, u.id
-> Nested Loop (cost=0.00..60.39 rows=248 width=195)
-> Seq Scan on tbl_users u (cost=0.00..8.16 rows=1 width=4)
Filter: ((id = 1000) AND (department_id = 10))
-> Seq Scan on tbl_tasks s (cost=0.00..49.75 rows=248 width=191)
Filter: ((parent_id IS NULL) AND (head_of = 1000) AND (status = '1'::smallint))