次の MySQL クエリを最適化しようとしています。
SELECT
`l`.`id` AS `l__id`, `l`.`latitude` AS `l__latitude`, `l`.`longitude` AS `l__longitude`, `l`.`name` AS `l__name`, `f`.`id` AS `f__id`, `f`.`day` AS `f__day`, `f`.`temperature_low` AS `f__temperature_low`, `f`.`temperature_high` AS `f__temperature_high`, `c`.`id` AS `c__id`, `c`.`name` AS `c__name`
FROM `location` `l`
INNER JOIN `forecast` `f` ON `l`.`id` = `f`.`location_id`
INNER JOIN `condition` `c` ON `f`.`condition_id` = `c`.`id`
WHERE (
`f`.`day` IN ('2012-12-28', '2012-12-29') AND
EXISTS (
SELECT
`f2`.`id` AS `f2__id`
FROM `forecast` `f2`
WHERE (
`f2`.`location_id` = `l`.`id` AND `f2`.`day` = "2012-12-28" AND `f2`.`condition_id` IN (6, 7, 9, 10, 11, 12, 13, 14, 18) AND `f2`.`temperature_high` <= 30 AND `f2`.`temperature_low` >= 0
)
) AND
EXISTS (
SELECT
`f3`.`id` AS `f3__id`
FROM `forecast` `f3`
WHERE (
`f3`.`location_id` = `l`.`id` AND `f3`.`day` = "2012-12-29" AND `f3`.`condition_id` IN (6, 7, 9, 10, 11, 12, 13, 14, 18) AND `f3`.`temperature_high` <= 30 AND `f3`.`temperature_low` >= 0
)
)
AND `l`.`latitude` IS NOT NULL AND `l`.`longitude` IS NOT NULL
);
EXPLAIN を実行すると、次の出力が得られます。
+----+--------------------+-------+--------+--------------------------------------+-----------------+---------+------------------------+------+----------------------------------------------+
| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |
+----+--------------------+-------+--------+--------------------------------------+-----------------+---------+------------------------+------+----------------------------------------------+
| 1 | PRIMARY | f | range | location_id_idx,condition_id_idx,day | day | 3 | NULL | 1298 | Using where; Using temporary; Using filesort |
| 1 | PRIMARY | l | eq_ref | PRIMARY | PRIMARY | 8 | weather.f.location_id | 1 | Using where |
| 1 | PRIMARY | c | eq_ref | PRIMARY | PRIMARY | 8 | weather.f.condition_id | 1 | |
| 3 | DEPENDENT SUBQUERY | f3 | ref | location_id_idx,condition_id_idx,day | location_id_idx | 9 | weather.l.id | 276 | Using where |
| 2 | DEPENDENT SUBQUERY | f2 | ref | location_id_idx,condition_id_idx,day | location_id_idx | 9 | weather.l.id | 276 | Using where |
+----+--------------------+-------+--------+--------------------------------------+-----------------+---------+------------------------+------+----------------------------------------------+
問題は「whereの使用;一時的な使用;filesortの使用」とサブクエリであることは理解していますが、パフォーマンスのためにこれを書き直す方法がわかりません。
今後このような問題を解決するのに役立つヒントを事前にありがとうございます。
ピート