QUERY PLAN
Aggregate (cost=153.16..153.17 rows=1 width=8)
-> Sort (cost=135.35..138.32 rows=1187 width=228)
Sort Key: s.created_at
-> HashAggregate (cost=62.87..74.74 rows=1187 width=228)
Group Key: s.id, u.id
-> Hash Left Join (cost=9.24..56.93 rows=1187 width=16)
Hash Cond: (s.head_of = u.id)
-> Seq Scan on tbl_tasks s (cost=0.00..44.49 rows=1187 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)