问题
I was trying to implement a query, that for each userid, rank the score and backfill the rank field, so that
id | score | rank
1 | 100 | 0
1 | 200 | 0
1 | 300 | 0
2 | 100 | 0
2 | 200 | 0
3 | 200 | 0
will become
id | score | rank
1 | 100 | 3
1 | 200 | 2
1 | 300 | 1
2 | 100 | 2
2 | 200 | 1
3 | 200 | 1
I saw a similar question here MySQL update statement to store ranking positions
However, in my case, how can I do the 'group by id' for each id?
回答1:
It might not be the prettiest way, but you can easily do something like:
set @rank = 0;
set @prev = 0;
select id, score, IF (id = @prev, @rank := @rank + 1, @rank := 1), @prev := id
from scores
order by id, score;
I guess you want the update statement as well, and that would be:
set @rank = 0;
set @prev = 0;
update scores
set rank = IF(id = @prev, @rank := @rank + 1, @rank := 1),
id = (@prev := id)
order by id, score;
来源：https://stackoverflow.com/questions/38620515/mysql-update-statement-to-backfill-ranking-by-each-id