MySQL update statement to store ranking positions

问题:

I'm trying to get my head around a query and I just can't figure it out. I would appreciate if someone give me a pointer. As a simple example of what I'm trying to achieve, I have these records in the database

Score|Ranking
-------------
100  |0
200  |0
300  |0

And I would like the Ranking field to contain 1,2,3 based on who's got the highest score so the result should be:

Score|Ranking
-------------
100  |3
200  |2
300  |1

At the moment, I'm doing a for next loop for all these records but given that in reality that could be a few thousand - that could take forever! Does anyone have an idea on a magic query which would do this in one go?

回答1:

In MySQL, you can use row_number.

Here's an example of using it in a SELECT:

select @rownum:=@rownum+1 ‘rank’, p.* 
from player p, (SELECT @rownum:=0) r 
order by score desc;

If you INSERT INTO using a SELECT like this, you will get your rankings.

回答2:

Here's a way to do it:

SET @r=0;
UPDATE table SET Ranking= @r:= (@r+1) ORDER BY Score DESC;

/* use this if you just want to pull it from the db, but don't update anything */
SET @r=0;
SELECT *, @r:= (@r+1) as Ranking FROM table ORDER BY Score DESC;

回答3:

This creates an inline update statement that will rank your players incrementing by the variable @rc. I've used it many times in very similar cases, it works well and keeps it all on the DB side.

SET @rc = 0;
UPDATE players JOIN (SELECT @rc := @rc + 1 AS rank, id FROM players ORDER BY rank DESC)
AS order USING(id) SET players.rank = order.rank;

id is assumed to be the primary key for your players table.

回答4:

SET @r = 0;
UPDATE players JOIN (SELECT @r := @r + 1 AS rank, id FROM players ORDER BY rank DESC)
AS sorted USING(id) SET players.rank = sorted.rank;

回答5:

i'm showing you my way of doing it [for interval sql update functions]

select:

set @currentRank = 0,
    @lastRating = null,
    @rowNumber = 1;
select
    *,
    @currentRank := if(@lastRating = `score`, @currentRank, @rowNumber) `rank`,
    @rowNumber := @rowNumber + if(@lastRating = `score`, 0, 1) `rowNumber`,
    @lastRating := `score`
from `table`
order by `score` desc

update:

set @currentRank = 0,
    @lastRating = null,
    @rowNumber = 1;
update 
    `table` r
    inner join (
        select
            `primaryID`,
            @currentRank := if(@lastRating = `score`, @currentRank, @rowNumber) `rank`,
            @rowNumber := @rowNumber + if(@lastRating = `score`, 0, 1) `rowNumber`,
            @lastRating := `score`
        from `table`
        order by `score` desc
    ) var on
        var.`primaryID` = r.`primaryID`
set
    r.`rank` = var.`rank`

i did not make any performance checks on this one except for testing that it works