문제 link
https://www.hackerrank.com/challenges/15-days-of-learning-sql/problem
Code link
https://github.com/JamesJung01/Hackerrank_sql/blob/main/03_Hard/15_Days_of_Learning.sql
select submission_date , (SELECT COUNT(distinct hacker_id) FROM Submissions s2 WHERE s2.submission_date = s1.submission_date AND (SELECT COUNT(distinct s3.submission_date) FROM Submissions s3 WHERE s3.hacker_id = s2.hacker_id AND s3.submission_date < s1.submission_date) = dateDIFF(s1.submission_date , '2016-03-01')) , (select hacker_id from submissions s2 where s2.submission_date = s1.submission_date group by hacker_id order by count(submission_id) desc , hacker_id limit 1) as shit, (select name from hackers where hacker_id = shit) from (select distinct submission_date from submissions) s1 group by submission_date;