Q2 Hard

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 TMP,
(SELECT NAME FROM HACKERS WHERE HACKER_ID = TMP)
FROM
(SELECT DISTINCT SUBMISSION_DATE FROM SUBMISSIONS) S1
GROUP BY SUBMISSION_DATE;