SELECT catX.category
catX.interest
t1.user_id
t1.score
FROM
( SELECT category
, interest
FROM tableX
WHERE user_id = @user_id_we_are_interested_in --- specific user
ORDER BY interest DESC
LIMIT @X --- top @X categories per specific user
) AS catX
JOIN
tableX AS t1
ON t1.category = catX.category
LEFT JOIN
tableX AS t2
ON t2.category = t1.category
AND t2.score > t1.score
GROUP BY t1.category
, t1.user_id
HAVING COUNT(t2.score) < @N --- top @N users per category
ORDER BY catX.interest DESC
, t1.score DESC