mysql group by using filesort优化

1. 原join 连接语句

   SELECT SUM(video_flowers.number) AS num,video_flowers.flower_id,flowers.title,flowers.imageFROM`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` = 36GROUP BY `video_flowers`.`flower_id`

可以优化成

SELECT     vf.num, flowers.title, flowers.imageFROM    `flowers`

join    (SELECT         SUM(video_flowers.number) AS num, video_flowers.flower_id, video_flowers.video_post_id    FROM        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;

这样就没有using filesort 和using temporary

原文地址：https://www.cnblogs.com/jpfss/p/9186627.html