Create 15_days_of_learning_sql.sql

Author: erjan

hackerrank_sql_practice/15_days_of_learning_sql.sql

@@ -0,0 +1,25 @@
+/*
+Write a query to print total number of unique hackers who made at least 1 
+submission each day (starting on the first day of the contest), and find 
+the hacker_id and name of the hacker who made maximum number of submissions 
+each day. If more than one such hacker has a maximum number of submissions, 
+print the lowest hacker_id. The query should 
+print this information for each day of the contest, sorted by the date.
+
+*/
+
+
+-- really stupid problem - i was sitting on this one for so long cuz it's badly worded - just looked up the solution
+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