sql.sql

CREATE INDEX "index_looks_on_created_at" ON "looks" ("created_at")

explain select * 
from looks where looks.created_at = (select max(l.created_at) from looks l where l.user_id = looks.user_id) limit 5

--                                  QUERY PLAN                                 
--  ---------------------------------------------------------------------------
--   Limit  (cost=0.00..26.50 rows=1 width=24)
--     ->  Seq Scan on looks  (cost=0.00..26.50 rows=1 width=24)
--           Filter: (created_at = (SubPlan 1))
--           SubPlan 1
--             ->  Aggregate  (cost=1.25..1.26 rows=1 width=8)
--                   ->  Seq Scan on looks l  (cost=0.00..1.25 rows=1 width=8)
--                         Filter: (user_id = looks.user_id)
--  (7 rows)


explain
select * 
from looks left join looks l on l.created_at > looks.created_at and l.user_id = looks.user_id
where l.id is null

--                             QUERY PLAN                              
-- ---------------------------------------------------------------------
--  Hash Left Join  (cost=1.45..2.97 rows=1 width=48)
--    Hash Cond: (looks.user_id = l.user_id)
--    Join Filter: (l.created_at > looks.created_at)
--    Filter: (l.id IS NULL)
--    ->  Seq Scan on looks  (cost=0.00..1.20 rows=20 width=24)
--    ->  Hash  (cost=1.20..1.20 rows=20 width=24)
--          ->  Seq Scan on looks l  (cost=0.00..1.20 rows=20 width=24)