title: ID increment 0001 + 1 shows 2
body: <p>I've got simple database with IDs <code>0001</code>, <code>0002</code> etc.
  I have to get my last ID and add 1 at the end.</p>
  
  <p>I am saving it to <code>$_SESSION['part_number'] = $part_number + 1;</code> 
  I don't know why I get 2 result if the ID is <code>0001</code>.
  Same if the ID is <code>0010</code> etc, I would like to have it always LAST ID + 1 with the 00 at the front.</p>