title: Mysql query to find hackers who made at least 1 submission each day
body: <p>I want to find all the hackers who made at least 1 submission each day.</p>
  
  <p>Table looks like: id, date.</p>
  
  <pre><code>1, 2016-01-01
  2, 2016-01-01
  3, 2016-01-01
  1, 2016-01-02
  2, 2016-01-02
  1, 2016-01-03
  </code></pre>
  
  <p>So the output should be:
  1
  Since 1 has made submission on all the day.</p>
  
  <p>What I have tried is:</p>
  
  <pre><code>Select id from table 
  group by id
  having count(*)=3 /* Since number of days are 3 */
  </code></pre>
  
  <p>However this is incorrect because a hacker can make multiple submissions on a day. 
  Example where my query will fail:</p>
  
  <pre><code>1, 2016-01-01
  2, 2016-01-01
  3, 2016-01-01
  3, 2016-01-01
  3, 2016-01-01
  1, 2016-01-02
  2, 2016-01-02
  1, 2016-01-03
  </code></pre>
  
  <p>After this is solved, the original question is:</p>
  
  <p>Write a query to print total number of unique hackers who made at least 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</p>