WITH hacker_challenges AS ( SELECT hacker_id, COUNT(*) AS challenges_created FROM Challenges GROUP BY hacker_id),

max_challenges AS (SELECT MAX(challenges_created) AS max_challenges FROM hacker_challenges),

challenges_created_included AS (SELECT challenges_created FROM hacker_challenges group by challenges_created having count(challenges_created)=1),

challenges_result AS (
SELECT hacker_id, challenges_created FROM hacker_challenges  
WHERE challenges_created = (SELECT * FROM max_challenges) 
OR challenges_created IN (SELECT * FROM challenges_created_included))

SELECT t1.hacker_id,t2.name,t1.challenges_created 
FROM challenges_result AS t1 JOIN hackers AS t2 on t1.hacker_id=t2.hacker_id
ORDER BY t1.challenges_created DESC,t1.hacker_id;