title: Delete all rows but the latest date
body: <p>I've got this table <code>supp_props</code>:</p>
  
  <pre><code>supp_id | supp_dry_weight | supp_price | supp_date
  --------+-----------------+------------+------------ 
    22    |      88.00      |   27.50    | 2015-06-25   x delete
    22    |      89.00      |   28.00    | 2015-10-18       &lt; don't delete, while
    22    |      89.00      |   29.50    | 2015-12-20         this row here is in the future
    23    |      84.00      |   15.00    | 2015-06-23   x delete
    23    |      42.50      |   7.50     | 2015-06-25   x delete
    23    |      35.60      |   5.00     | 2015-06-29
    24    |      89.00      |   18.20    | 2015-06-25
    25    |      89.15      |   18.50    | 2015-08-05
    26    |      89.00      |   28.30    | 2015-06-25
  </code></pre>
  
  <p>And I want to delete all rows that are 'old', but there are some conditions:</p>
  
  <ul>
  <li>a row must be older than two weeks to be deleted.</li>
  <li>if there is no row with a more current date it shouldn't be deleted.</li>
  <li>There may be rows that are in the future, if so, this row shouldn't be seen as a 'more current' date (for the above rule).</li>
  </ul>
  
  <p>How can I achieve that with mysql?</p>