LeetCode 602. Friend Requests II: Who Has the Most Friends

602. Friend Requests II: Who Has the Most Friends

SELECT *
FROM (
SELECT id, SUM(num) AS num 
FROM (
SELECT requester_id AS id, COUNT(requester_id) AS num
FROM RequestAccepted
GROUP BY requester_id 

UNION ALL

SELECT accepter_id AS id, COUNT(accepter_id) AS num
FROM RequestAccepted
GROUP BY accepter_id
) AS TOT
GROUP BY id
ORDER BY 2 DESC
) AS STOT
LIMIT 1

 

조인인줄 알았는데 from 보다 select로 먼저 생각해보니 

friends 수를 세려면 requester_id 와 accepter_id 수를 동시에 count해야 될 것 같아서 

union all로 풀었더니 해결됐던!!

 

못풀고 있던 문제였는데 오늘 도전해보니 풀려서 기분 조와짐,,