Yii CDbCriteria和Model-> findAll,如何添加自定义列？

$criteria = new CDbCriteria;
$criteria->select = 'column1, column2, custom_column';
$criteria->addColumnCondition(array('custom_column' => 'custom_value'));
$result = Model::model()->findAll($criteria);

$result = Model::model()->findAll(array(
    'select' => 'column1, column2, custom_column',
    'condition' => 'custom_column = :custom_value',
    'params' => array(':custom_value' => 'custom_value'),
));