title: How can add a condtion to Yii CDbCriteria select?
body: <p>I use this codes.
  I want check if budget &lt; 0 select it.</p>
  
  <pre><code>$criteria = new CDbCriteria;
  $criteria-&gt;select = array('*', 'SUM(amount) as budget');
  $criteria-&gt;group = 'user_id';
  $debtors = Transactions::model()-&gt;findAll($criteria);
  </code></pre>
  
  <p>How can i add this condition?</p>