SELECT Hac.hacker_id,Hac.name FROM Submissions AS Sub 
JOIN Hackers AS Hac USING(hacker_id)
JOIN Challenges AS Cha USING (challenge_id) 
JOIN Difficulty AS Dif USING(difficulty_level)
WHERE Sub.score=Dif.score
GROUP BY Hac.hacker_id,Hac.name
HAVING COUNT(*) > 1
ORDER BY COUNT(*) DESC ,Hac.hacker_id