title: Display distinct users reaching specific count thresholds
body: <p>Here's my table, showing user names and the timestamp they scored a point: </p>
  
  <pre><code>id  user    date
  1   Aaron   23/02/2012 22:44
  2   Betty   23/02/2012 22:47
  3   Carlos  24/02/2012 16:01
  4   David   28/02/2012 11:40
  5   David   28/02/2012 12:32
  6   David   28/02/2012 16:59
  7   Aaron   2/03/2012 13:46
  8   Aaron   30/03/2012 18:37
  9   Betty   30/03/2012 19:58
  10  Emma    9/04/2012 6:49
  11  Emma    9/04/2012 13:19
  12  Emma    9/04/2012 18:20
  13  Emma    9/04/2012 20:46
  14  Aaron   10/04/2012 15:47
  15  Betty   10/04/2012 19:15
  16  Betty   10/04/2012 20:40
  17  Carlos  11/04/2012 9:44
  18  Carlos  11/04/2012 20:01
  19  David   11/04/2012 23:17
  20  David   12/04/2012 17:09
  </code></pre>
  
  <p>And here is the results table I am <em>trying</em> to achieve, i.e. an x axis showing month-year, and a y axis displaying the number of users who reached a certain points threshold <em>within that month</em>:</p>
  
  <pre><code>date    1 point First time? 2 points    First time? 3 points    First time? 4 points    First time?     Total
  Feb-12  A,B,C   A,B,C                               D           D                                       4
  Mar-12  B                   A           A                                                               3
  Apr-12  A,B,C               B,C,D       B,C,D                               E           E               4
  </code></pre>
  
  <p>I've only got as far as calculating the total number of points and the total number of distinct scorers within a given month:</p>
  
  <pre><code>SELECT DISTINCT CONCAT (MONTHNAME(date), ' ', YEAR(date)) as 'date', COUNT(id) as total_points, COUNT(distinct referrer_id) as number_of_scorers
  from points
  group by CONCAT (MONTH(date), ' ', YEAR(date))
  order by YEAR(date), MONTH(date)
  </code></pre>
  
  <p>which is only giving me:</p>
  
  <pre><code>date    total_points    number_of_scorers
  Feb-12  6               4
  Mar-12  3               3
  etc.
  </code></pre>
  
  <p>So my questions are: </p>
  
  <ol>
  <li>How can I amend the query to show me which users reached each point threshold within each month? </li>
  <li>How can I amend the query to show me which users reached each point threshold <em>for the first time</em> within that month?</li>
  </ol>
  
  <p>Thanks</p>