title: What do the “l” and “p” mean in this SQL statement?
body: <p>I have the following statement which filters out a result from multiple tables.  I am not quite understanding the <code>p</code> after <code>tablename</code> and the <code>l</code> after <code>anothertablename</code>.  Are they generic or purposeful?</p>
  
  <p><code>SELECT id, title, l.id, username FROM tablename p JOIN anothertablename l ON (l.id = p.id) WHERE p.id='15' LIMIT 1</code></p>