QUERY PLAN
Aggregate (cost=153.61..153.62 rows=1 width=8)
-> Sort (cost=135.75..138.73 rows=1191 width=228)
Sort Key: s.created_at
-> HashAggregate (cost=62.99..74.90 rows=1191 width=228)
Group Key: s.id, u.id
-> Hash Left Join (cost=9.24..57.04 rows=1191 width=16)
Hash Cond: (s.head_of = u.id)
-> Seq Scan on tbl_tasks s (cost=0.00..44.58 rows=1191 width=24)
Filter: (parent_id IS NULL)
-> Hash (cost=7.44..7.44 rows=144 width=4)
-> Seq Scan on tbl_users u (cost=0.00..7.44 rows=144 width=4)