[HackerRank] Challenges

https://www.hackerrank.com/challenges/challenges/problem?isFullScreen=true 

Challenges | HackerRank

with cnt as(
    select h.hacker_id
        , h.name
        , count(challenge_id) challenges_created
    from hackers h left join challenges c
        on h.hacker_id = c.hacker_id
    group by h.hacker_id, h.name
    order by 3 desc, 1
    )

select *
from cnt
where challenges_created in (
    select max(challenges_created)
    from cnt
    union
    select challenges_created
    from cnt
    group by challenges_created
    having count(*) = 1
    )