title: MySQL query order by multiple items
body: <p>Is it possible to order by multiple rows?</p>
  <p>I want my users to be sorted by <code>last_activity</code>, but at the same time, I want the users with pictures to appear before the ones without</p>
  <p>Something like this:</p>
  <pre><code>SELECT some_cols
  FROM `prefix_users`
  WHERE (some conditions)
  ORDER BY last_activity, pic_set DESC;
  </code></pre>