QUERY PLAN
Aggregate (cost=61.40..61.41 rows=1 width=8)
-> Sort (cost=60.86..60.95 rows=36 width=228)
Sort Key: s.created_at
-> HashAggregate (cost=59.57..59.93 rows=36 width=228)
Group Key: s.id, u.id
-> Nested Loop (cost=0.00..59.39 rows=36 width=16)
-> Seq Scan on tbl_users u (cost=0.00..8.16 rows=1 width=4)
Filter: ((id = 1001) AND (department_id = 4))
-> Seq Scan on tbl_tasks s (cost=0.00..50.87 rows=36 width=24)
Filter: ((parent_id IS NULL) AND (head_of = 1001) AND (status = '1'::smallint))