Yii PDO::FETCH_GROUP

gistfile1.php

<?php
$sth = Yii::app()->getDb()->getPdoInstance()->prepare('
    SELECT
        when_created,
        type_id,
        amount
    FROM rates
    WHERE employee_id = :employee_id
');
$sth->execute(array(
    ':employee_id' => $employee_id
));
$rows = $sth->fetchAll(PDO::FETCH_GROUP | PDO::FETCH_ASSOC);
vd($rows);