42. Find Followers Count
https://leetcode.com/problems/find-followers-count/description/
Write a solution that will, for each user, return the number of followers. Return the result table ordered by user_id in ascending order.
Select user_id, count(follower_id) followers_count From Followers group by user_id order by user_id
오랜만에 정렬(order by)이 문제로 제시..!!