Re: Help speeding up this query - maybe need another index?

Pat Maddox wrote:
> Here's my SQL query.  I don't think it's too gigantic, but it is kind
> of beastly:
>
> SELECT COUNT(r) FROM trainer_hand_results r, trainer_scenarios s,
> trainer_scenario_stats stats WHERE r.user_id=1 AND
> r.trainer_scenario_id=s.id AND s.id=stats.trainer_scenario_id AND
> r.action=stats.correct_action;
>
> When I EXPLAIN it, I get:
>
> Aggregate  (cost=18.12..18.13 rows=1 width=32)
>   ->  Nested Loop  (cost=0.00..18.12 rows=1 width=32)
>         ->  Nested Loop  (cost=0.00..12.28 rows=1 width=40)
>               Join Filter: (("outer"."action")::text =
> ("inner".correct_action)::text)
>               ->  Seq Scan on trainer_hand_results r
> (cost=0.00..6.56 rows=1 width=181)
>                     Filter: (user_id = 1)
>               ->  Index Scan using
> trainer_scenario_stats_trainer_scenario_id_index on
> trainer_scenario_stats stats  (cost=0.00..5.71 rows=1 width=149)
>                     Index Cond: (stats.trainer_scenario_id =
> "outer".trainer_scenario_id)
>         ->  Index Scan using trainer_scenarios_pkey on
> trainer_scenarios s  (cost=0.00..5.82 rows=1 width=4)
>               Index Cond: ("outer".trainer_scenario_id = s.id)
> (10 rows)
>
> I don't have a lot of experience with getting queries to go faster.
> The things that jump out at me though are two nested loops and a
> sequential scan.  What could I do to speed this up?

Have you analyzed the tables in question?

Post the result of 'explain analyze' rather than just explain.

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