una cosa del genere magari
codice:
$stringa='';
$query = "SELECT * FROM ordini WHERE evaso = 'x' ORDER BY id DESC";
$result = mysql_query($query);
while ($row = mysql_fetch_array($result)){
 $stringa.="ordine {$row['nr_ordine']}, ";
}
mysql_free_result($result); 

$stringa=substr($stringa,0,-2);
echo $stringa;