QUERY PLAN
Limit (cost=62.40..62.42 rows=10 width=195)
-> Sort (cost=62.40..62.85 rows=181 width=195)
Sort Key: s.created_at
-> HashAggregate (cost=56.67..58.48 rows=181 width=195)
Group Key: s.id, u.id
-> Hash Join (cost=8.07..55.77 rows=181 width=195)
Hash Cond: (s.head_of = u.id)
-> Seq Scan on tbl_tasks s (cost=0.00..44.49 rows=1187 width=191)
Filter: (parent_id IS NULL)
-> Hash (cost=7.80..7.80 rows=22 width=4)
-> Seq Scan on tbl_users u (cost=0.00..7.80 rows=22 width=4)
Filter: (department_id = 10)