CODEWITHSUNDEEP
phpmysqlranking
Jack
Jack

Reputation: 3799

Calculating rank in PHP/MySQL

I've got a table in MySQL lets just say for example its got two fields Username, GameName and Score. I want to calculate the rank of a user for an indivudal game name so I could do the query

SELECT * FROM scores WHERE `GameName` = 'Snake' ORDER BY `Score` DESC

to get a list of all users in order of highest to lowest and assign a number to each user.

But is there an easier way to get the rank for an indivdual user rather than selecting the entire table as that doesn't seem too efficient.

Thanks

Upvotes: 2

Views: 17858

Answers (8)

bindasarpan
bindasarpan

Reputation: 3

Following query is using rank function, this can be materialised as well:

WITH game_rank AS(
    SELECT 
        user_id, 
        gameName, 
        RANK() OVER (
            PARTITION BY gameName
            ORDER BY score DESC
        ) order_value_rank
    FROM
        scores
)
SELECT 
    * 
FROM 
    game_rank
WHERE 
    gameName = "Snake";

Upvotes: 0

c9s
c9s

Reputation: 1917

My one query solution:

select @rank:=@rank+1 AS Rank,L1.* from 
    (select @rank:=0) as L2,
    (select i.*,count(*) as sum 
        FROM 
        transactions t
        LEFT JOIN companies c on (c.id = t.company_id)  
        LEFT JOIN company_industries ci on (c.id = ci.company_id)  
        LEFT JOIN industries i on (ci.industry_id = i.id)
        GROUP by i.name 
        ORDER BY sum desc ) as L1;

Upvotes: 1

symcbean
symcbean

Reputation: 48357

You can't get away from reading a lot of the data in the table - but you don't need to haul it all the way back to your processing script:

SELECT COUNT(*)
FROM scores 
WHERE `GameName` = 'Snake'
AND user=$some_user;

(since you probably want the first person to have a rank of '1' rather than '0', increment the result).

However if you need to run the query often, it's worth maintaining a materialized view of the sorted results.

Upvotes: 2

Chris Heald
Chris Heald

Reputation: 62648

If you want overall rankings, you unfortunately have to sort the whole table. Simply put, you cannot know someone's rank in the table without knowing the other ranks in the table.

That said, if you are worried about performance, there's a fairly easily solution here - cache the result of your ranking query (maybe into another a MySQL table!), and query that for all your reads. When someone posts a new score, recalculate your temporary table. You can periodically flush all records under a certain rank (say, anyone ranking under 100 gets removed from the scores table) to keep recomputations fast, since nobody would ever climb in rank after being knocked down by a higher score.

# Create your overall leaderboards once
create table leaderboards (rank integer primary key, score_id integer, game varchar(65), user_id integer, index game_user_id_idx (game, user_id))


# To refresh your leaderboard, we'll query the ranks for the game into a temporary table, flush old records from scores, then copy
# the new ranked table into your leaderboards table.
# We'll use MySQL's CREATE TABLE...SELECT syntax to select our resultset into it directly upon creation.
create temporary table tmp_leaderboard (rank integer primary key auto_increment, score_id integer, game varchar(65), user_id integer)
  select ID, GameName, UserID, from scores where GameName = '$game' order by score desc;

# Remove old rankings from the overall leaderboards, then copy the results of the temp table into it.
delete from leaderboards where game = '$game';
insert into leaderboards (rank, score_id, game, user_id)
  select rank, score_id, game, user_id from tmp_leaderboard;

# And then clean up the lower scores from the Scores table
delete from scores join tmp_leaderboard on scores.id = tmp_leaderboard.score_id, scores.GameName = tmp_leaderboard.game where tmp_leaderboard.rank < 100;

# And we're done with our temp table
drop table tmp_leaderboard;

Then, whenever you want to read a rank for a game:

select rank from leaderboards where game = '$game' and user_id = '$user_id';

Upvotes: 4

Jared Farrish
Jared Farrish

Reputation: 49188

Be interesting to see if there were a way to get the rank in MySQL, but here is how you could do it in PHP:

function getRank($user, $game, $limit=50) {
    $sql = "
SELECT @rank:=@rank+1 AS Rank, User, GameName
FROM scores, (SELECT @rank:=1) AS i
WHERE `GameName` = '$game' 
ORDER BY `Score` DESC
LIMIT 0, $limit
";

    $result =  mysql_query($sql);

    while ($row = mysql_fetch_assoc($result)) {
        if ($row['User'] == $user) {
            return $row['Rank'];
        }
    }

    return -1;
}

Note, I put the limit in there because otherwise you will not get but 30 results back. And it returns -1 if the player is unranked.

Upvotes: 1

ipsum
ipsum

Reputation: 1052

You should add indexes to GameName and Score. (And don't forget to escape the GameName before inserting in the query => mysql_real_escape_string). @Bryan: shouldn't it be "AND" than "&&" ?

Upvotes: 0

Bryan
Bryan

Reputation: 347

SELECT * FROM scores WHERE 'GameName' = 'Snake' && userID = '$userID' ORDER BY 'Score' DESC

Upvotes: 1

Muhamad Bhaa Asfour
Muhamad Bhaa Asfour

Reputation: 1035

get the user id from your users table and use it in your query


SELECT * FROM scores WHERE `GameName` = 'Snake' 
and `youruseridfield` = '$useridvalue'
ORDER BY `Score` DESC

Upvotes: 1

Related Questions