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我期待優化下面MySQL查詢:MySQL查詢優化 - 子查詢和使用哪裏;使用臨時;使用文件排序
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
);
運行的EXPLAIN給出了下面的輸出:
+----+--------------------+-------+--------+--------------------------------------+-----------------+---------+------------------------+------+----------------------------------------------+
| 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 |
+----+--------------------+-------+--------+--------------------------------------+-----------------+---------+------------------------+------+----------------------------------------------+
我明白,問題是「在那裏使用;使用臨時;使用filesort「和子查詢,但我不確定如何重新寫這個表現。
預先感謝任何能幫助我解決未來這類問題的指針。
皮特
感謝您的新鮮眼睛bmewsing。你完全正確,我不需要每天循環創建子查詢,因爲每天的條件和溫度是相同的。我認爲能夠在不同的日子選擇不同的條件是我遺留下來的。乾杯! – 2013-02-16 11:51:46