WITH
  cte1 AS   (   SELECT s.submission_date, s.submission_id, s.hacker_id, h.name
                    , DAY(s.submission_date) AS day_num
                    , DENSE_RANK() OVER(PARTITION BY s.hacker_id ORDER BY s.submission_date) AS rnk
                FROM submissions s
                JOIN hackers h ON h.hacker_id = s.hacker_id
                WHERE s.submission_date BETWEEN '2016-03-01' AND '2016-03-15' )
, cte2 AS   (   SELECT submission_date, COUNT(DISTINCT hacker_id) AS unique_h_count
                FROM cte1
                WHERE day_num = rnk
                GROUP BY submission_date )

, cte3 AS   (   SELECT submission_date, hacker_id, COUNT(submission_id) AS s_count
                FROM cte1
                GROUP BY submission_date, hacker_id )
, cte4 AS   (   SELECT *, ROW_NUMBER() OVER(PARTITION BY submission_date ORDER BY s_count DESC, hacker_id) AS rn
                FROM cte3 )

SELECT cte4.submission_date, cte2.unique_h_count, cte4.hacker_id, h.name
FROM cte4
JOIN hackers h ON h.hacker_id = cte4.hacker_id
JOIN cte2 ON cte2.submission_date = cte4.submission_date
WHERE rn = 1