title: Multiple SQL ORDER BY statements take the same time to execute
body: <p>I have two sql statements in pgsql:</p>
  
  <pre><code>SELECT * FROM persdata ORDER BY 1;
  SELECT * FROM persdata ORDER BY 3, 2, 1;
  </code></pre>
  
  <p>Both take the same amount of time (cost) to execute. Why is that?</p>