1. 原join 连接语句

   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`

可以优化成

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_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