- Basic Join > Joins+Groupby+Having : Watch the keys
https://www.hackerrank.com/challenges/full-score/problem?isFullScreen=true
select h.hacker_id id, h.name nm
from hackers h
left join submissions s
on h.hacker_id = s.hacker_id
left join challenges c
on s.challenge_id = c.challenge_id
left join difficulty d
on c.difficulty_level = d.difficulty_level
where s.score = d.score
group by h.hacker_id, h.name
having count(s.submission_id) > 1
order by count(s.submission_id) desc, h.hacker_id asc
yozzum