title: SQL - insert and limit the number of entries
body: <p>I have a table that represents a user's entries:</p>
  
  <pre><code>User_ID | Entry_ID
  </code></pre>
  
  <p>Now I want to store only the last 20 entries (for example).</p>
  
  <p>What would be the best way to insert new entries while keeping the maximum number of entries per user at 20 (new entries will replace oldest entries) ?</p>
  
  <p>I need to be able to insert also a list of items to replace the old ones (if possible, to avoid multiple SQL requests)</p>