CDbCriteria

    $criteria = new CDbCriteria();
    $criteria->select = '*, SUM(IF(type = 1, 1, 0)) AS sellersCnt';
    $criteria->with = array('profile');
    $criteria->together = TRUE;
    $sellersArray = User::model()->findAll($criteria);

    $criteria->select = array("SUM(price) as price");
    $criteria->with = array();
    $result = self::model()->find( $criteria );
    return $result->price;

Подробнее: http://www.yiiframework.com/doc/api/1.1/CDbCriteria#distinct-detail

• select
• alias = "t" (Алиас основной таблицы)
• distinct = true, false (SELECT DISTINCT)
• join = "join order o on t.order_id = o.id"
• condition = "t.client_id=1"
• group
• having
• order
• limit

• params = array()

• together
• with