原join 連接語句

SELECT
SUM(video_flowers.number) AS num,
video_flowers.flower_id,
flowers.title,
flowers.image
FROM
`video_flowers`
JOIN
`flowers` ON `video_flowers`.`flower_id` = `flowers`.`id`
JOIN
`video_posts` ON `video_flowers`.`video_post_id` = `video_posts`.`id`
WHERE
`video_posts`.`user_id` = 36
GROUP BY `video_flowers`.`flower_id`

可以優(yōu)化成

SELECT
vf.num, flowers.title, flowers.image
FROM
`flowers`

join
(SELECT
SUM(video_flowers.number) AS num, video_flowers.flower_id, video_flowers.video_post_idFROM
video_flowers
GROUP BY `video_flowers`.`flower_id`) AS vf ON `vf`.`flower_id` = `flowers`.`id`
join `video_posts` on `video_posts`.`id` = vf.`video_post_id`
where video_posts.user_id = 36;

這樣就沒有using filesort 和using temporary

總結(jié)

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