Select
    h.hacker_id,
    h.name
From hackers h
Join submissions s
    on h.hacker_id = s.hacker_id
Join challenges c
    on s.challenge_id = c.challenge_id
Join difficulty d
    on c.difficulty_level = d.difficulty_level
Where s.score = d.score
Group by h.hacker_id, h.name
Having count(distinct(s.challenge_id)) > 1
Order by count(distinct(c.challenge_id)) desc, h.hacker_id asc;