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SELECT hackers.hacker_id, hackers.name FROM hackers
INNER JOIN submissions ON hackers.hacker_id =submissions.hacker_id INNER JOIN difficulty ON submissions.score = difficulty.score
JOIN challenges ON submissions.challenge_id = challenges.challenge_id AND difficulty.difficulty_level = challenges.difficulty_level
GROUP BY hackers.hacker_id, hackers.name HAVING count(submissions.hacker_id) > 1 ORDER BY count(submissions.submission_id) DESC, submissions.hacker_id;