SELECT hacker_id, name FROM (
    SELECT H.hacker_id, name, COUNT(challenge_id) AS ct
    FROM Submissions AS S
    LEFT JOIN Hackers AS H USING (hacker_id)
    LEFT JOIN Challenges USING (challenge_id)
    LEFT JOIN Difficulty AS D USING (difficulty_level)
    WHERE S.score = D.score
    GROUP BY H.hacker_id, name HAVING ct > 1
    ORDER BY ct DESC, H.hacker_id ASC
) AS rankings;