MySQL group by using Filesort optimization

1. The original JOIN Connection statement

   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 '= $
   GROUP  by ' Video_flowers '.' flower_id '

can be optimized into

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 ') asVf on ' VF '.' flower_id '=' Flowers '.' id '
    Join ' video_posts '  on ' video_posts '.' id '= VF.' video_post_id '
    wherevideo_posts.user_id = $;

Thus there is no using filesort and using temporary

MySQL group by using Filesort optimization