MySQL sum ranking, group by genre, limit 10

Question

I have MySQL tables like these and I would like to calculate the TOP10 for each genre:

• rankings_2016 (trackId, genreId, ranking, timestamp)
• genres (genreId, genreName)
• tracks (trackId, trackName, genreId)
• artists (artistId, artistName)
• artists_tracks (artistId, trackId)

I would like to get TOP10 rankings for each genre, for every track and for every artist.

A track or an artist could have up to 2 genres. Ranking could be the same. Just to get the idea with LIMIT 2:

  genreId | trackId | ranking
 ---------------------------------
   0         1111      100
   0         2222       99
   1         1111      100
   1         2222       99

  genreId | artistId | ranking
 ---------------------------------
   0         1111      100
   0         2222       99
   1         1111      100
   1         2222       99

The only solution I found is getting everything in a table and then LIMIT 10 in the page, but it's killing my database in terms of size (I have limited resources).

For the tracks I wrote this:

SELECT trackId, genreId, @newRank := SUM(ranking) as ranking
FROM rankings_2016
WHERE timestamp >= ( select unix_timestamp('2016-01-01') )
AND timestamp <= ( select unix_timestamp('2016-12-31') )
GROUP BY trackId, genreId

For the artists:

SELECT artistId, genreId, @newRank := SUM(a1.ranking) as ranking
FROM rankings_2016 a1
LEFT JOIN artists_tracks a2
ON a1.trackId = a2.trackId
WHERE timestamp >= ( select unix_timestamp('2016-01-01') )
AND timestamp <= ( select unix_timestamp('2016-12-31') )
GROUP BY artistId, genreId

Thank all in advance for your hints.

---

UPDATE

The logic in general (and accepted reply) requires good indexes and performant server.

ARTISTS in my case failed with error 500 unless I increased CPU. In general replacing LEFT with INNER saves 1 second.

Answer 1

Consider a correlated count subquery to rank order the rankings by Artist / Track / Genre groupings. Then use this rank calculated column in outer query to filter for top 10 per grouping:

Artist Ranking (top 10 rankings per artist and genre)

SELECT main.artistId, main.genreId, main.ranking
FROM
 (
   SELECT a.artistId, r.genreId, r.ranking,
          (SELECT COUNT(*) FROM rankings_2016 subr
           LEFT JOIN artists_tracks suba ON subr.trackId = suba.trackId
           WHERE suba.artistId = a.artistId
           AND subr.genreId = r.genreId
           AND subr.ranking >= r.ranking) AS rn
   FROM rankings_2016 r
   LEFT JOIN artists_tracks a ON r.trackId = a.trackId
   WHERE r.timestamp BETWEEN ( select unix_timestamp('2016-01-01') )
                         AND ( select unix_timestamp('2016-12-31') ) 
 ) AS main

WHERE main.rn <= 10

Track Ranking (top 10 rankings per track and genre)

SELECT main.trackId, main.genreId, main.ranking
FROM
 (
   SELECT r.trackId, r.genreId, r.ranking,
          (SELECT COUNT(*) FROM rankings_2016 subr               
           WHERE subr.genreId = r.genreId
           AND subr.trackId = r.trackId
           AND subr.ranking >= r.ranking) AS rn
   FROM rankings_2016 r
   WHERE r.timestamp BETWEEN ( select unix_timestamp('2016-01-01') )
                         AND ( select unix_timestamp('2016-12-31') ) 
 ) AS main

WHERE main.rn <= 10