select hacker_id,name,sum(max_score) as total_score
from (
    select s.hacker_id,h.name,challenge_id,max(score) as max_score
from submissions s
left join hackers h
    on s.hacker_id=h.hacker_id
group by s.hacker_id,h.name,challenge_id
having max(score)>0) as max_count
group by hacker_id,name
order by total_score desc,hacker_id asc