/*
MSSQL
*/
with cte as (
select s.hacker_id, h.name, s.challenge_id, s.score,
    row_number() over(partition by s.hacker_id, s.challenge_id order by s.score desc) as rn
    from submissions s join hackers h
    on s.hacker_id = h.hacker_id
)
select hacker_id, name,
    sum(score) as total_score
from cte
    where rn = 1
    group by hacker_id, name
    having sum(score) > 0
    order by total_score desc, hacker_id asc