mysql rank by column value grouped by column value

Question

I am trying to figure out how to rank based on 2 different column numbers in laravel but raw mysql will do. I have a list of videos, these videos are inside of competitions and are given votes if someone likes the video. Each video will have a vote number and a competition number. I am trying to rank based on votes within competition. So for example below I have competition 8, I need the rank of all the videos in that competition based on votes. I then need the same for competition 5 etc.

  |rank|votes|competition|
  ------------------
  |  1 | 100 | 8   |
  ------------------
  |  2 |  50 | 8   |
  ------------------
  |  3 |  30 | 5   |
  ------------------
  |  1 | 900 | 5   |
  ------------------
  |  2 |  35 | 5   |
  ------------------

I have tried various group and selectby methods but nothing seems to work, any ideas?

Answer 1

In Mysql you can use user-defined variables to calculate rank,case statement checks if competition is same as the previous row then increment rank by one if different then assign 1 an order by is needed to have correct rank for the video

 SELECT t.*,
   @current_rank:= CASE WHEN @current_rank = competition 
             THEN  @video_rank:=@video_rank +1 
             ELSE @video_rank:=1 END  video_rank,
   @current_rank:=competition
FROM t ,
(SELECT @video_rank:=0,@current_rank:=0) r   
  ORDER BY competition desc, votes desc

See Demo

If you are confused with the last extra column you can use a subselect

See Demo

Answer 2

You can use windowing functions:

select
    competition, votes, rank() over (partition by competition order by votes desc) as rank
from
    table1