What wrong am I doing now?

mysql> SELECT DATE_FORMAT(dato, '%e-%c-%Y') FROM transportdokument WHERE
dato >= '2013-07-20' AND dato <= '2013-07-24' GROUP BY dato DESC;
+-------------------------------+
| DATE_FORMAT(dato, '%e-%c-%Y') |
+-------------------------------+
| 24-7-2013                     |
| 23-7-2013                     |
+-------------------------------+
2 rows in set (0.00 sec)

mysql>


// My PHP code looks like this.
// -----------------------------------------
$sql = "SELECT DATE_FORMAT(dato, '%e-%c-%Y') FROM transportdokument WHERE
dato >= '2013-07-20' AND dato <= '2013-07-24' GROUP BY dato DESC";
$resultat = mysql_query($sql, $tilkobling) or die(mysql_error());

while($rad = mysql_fetch_array($resultat)){
$dato = $rad['dato'];
var_dump($dato);

I gott NULL,NULL here and believe it is something with my PHP Source that
is wrong when using DATE_FORMAT. As you see above it work in terminal.

I hope this not is off-topic for the list. If so, I am sorry for it and
hope you can give me advice about a good MySQL list for newbie's.

Thanks again for your help!

Karl