如何为Yii CDbCriteria选择添加条件？

I use this codes. I want check if budget < 0 select it.

$criteria = new CDbCriteria;
$criteria->select = array('*', 'SUM(amount) as budget');
$criteria->group = 'user_id';
$debtors = Transactions::model()->findAll($criteria);

How can i add this condition?

use

$criteria = new CDbCriteria;
$criteria->select = array('*', 'SUM(amount) as budget');
$criteria->having = 'budget < 0 ' ;
$criteria->group = 'user_id';
$debtors = Transactions::model()->findAll($criteria);