关于Createcommand的一点疑问

$sql = "SELECT  a.uname AS email, SUM(c.goodsprice*31*c.goodsnum) AS money, FROM_UNIXTIME(d.`addtime`,'%Y/%m') AS buytime
                FROM dg_users a, dg_big_order b, dg_order c, dg_sendorder d
                WHERE a.uname IN (:uname) AND b.old_new = 2
                  AND c.state <> '6'
                  AND d.state IN (2, 3)
                  AND a.uid = b.uid
                  AND b.ooid = c.ooid
                  AND c.ooid = d.ooid
                  GROUP BY email, buytime
                  ORDER BY buytime desc";

$names = "'a@abc.com','b@abc.com','c@abc.com'";
$command2 = Yii::app()->db->createCommand($sql);
$command2->bindValue(':uname',$names)
$command2->queryAll();

$names = "'a@abc.com','b@abc.com','c@abc.com'";
$sql = str_replace(':uname',$names,$sql);
$command2 = Yii::app()->db->createCommand($sql);
$command2->queryAll();