CDbExpression

NOW()

Yii::app()->db->createCommand()->insert('table', array(    
    'title'=> 'title1',    
    'description'=> 'description1',  
    'date_now' => new CDbExpression('NOW()'),  
));

DATE_FORMAT()

$allRecords2 = Yii::app()->db->createCommand()    
    ->select(array(
        'title', 
        'description', 
        new CDbExpression("DATE_FORMAT(date_now, '%Y-%m-%d') AS dateNowFormat")))   
    ->from('table')     
    ->queryAll();

или

$dateNow = new CDbExpression("DATE_FORMAT(date_now, '%Y-%m-%d') AS dateNowFormat");  
 
$allRecords = Yii::app()->db->createCommand()    
    ->select('title, description, '.$dateNow.'')   
    ->from('table')     
    ->queryAll();

или

$criteria = new CDbCriteria();    
$criteria->select = new CDbExpression("DATE_FORMAT(date_now, '%Y-%m-%d') AS dateNowFormat");