SELECT joint.hack, h.name, sum(joint.max_score) total_score --Return the values, hacker_id, name and sum of max scores

FROM (SELECT s.hacker_id as hack, max(s.score) max_score -- Create a nested select to return the id and max score

FROM SUBMISSIONS s

WHERE s.score >0 -- Ensure value is greater than zero

GROUP BY s.hacker_id, s.challenge_id -- Aggregate by hacker_id, and challenge_id

) joint

INNER JOIN HACKERS h

ON joint.hack = h.hacker_id -- Join to the hacker table to get names

GROUP BY joint.hack, h.name -- Group by both the hacker_id and name. Should be one to one relation

ORDER BY total_score desc, joint.hack -- Order by appropriate value