select h.hacker_id,h.name,sum(s.score)
from hackers h join Submissions s on h.hacker_id=s.hacker_id 
where 
score in (select max(score) from Submissions group by hacker_id,challenge_id)
group by h.hacker_id,h.name,s.challenge_id
having sum(s.score)>0
order by sum(s.score) desc, h.hacker_id asc``