select hackers.hacker_id
, name
, sum(score) total_score
from hackers
inner join (
            select hacker_id, max(score) as score
            from submissions
            group by hacker_id, challenge_id) as submissions on hackers.hacker_id = submissions.hacker_id
group by hackers.hacker_id, name
HAVING SUM(score) > 0
order by sum(score) desc, hacker_id