On 6/13/06, Chris <dmagick@xxxxxxxxx> wrote:
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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Here is the result from EXPLAIN ANALYZE on that query:
Aggregate (cost=18.12..18.13 rows=1 width=32) (actual
time=4.924..4.925 rows=1 loops=1)
-> Nested Loop (cost=0.00..18.12 rows=1 width=32) (actual
time=0.243..4.878 rows=15 loops=1)
-> Nested Loop (cost=0.00..12.28 rows=1 width=40) (actual
time=0.222..4.613 rows=15 loops=1)
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) (actual time=0.039..1.302 rows=285
loops=1)
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)
(actual time=0.009..0.009 rows=0 loops=285)
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) (actual
time=0.012..0.014 rows=1 loops=15)
Index Cond: ("outer".trainer_scenario_id = s.id)
Total runtime: 5.494 ms
(11 rows)
