[PHP & MySQL] Piccolo problema "virgola"

[Leilond]

function UsersOnline(){
    include"config.inc.php";
    mysql_select_db($database_name, $conn) or die ("Errore nel selezionare il db: " . mysql_error());
    $sql = "SELECT * FROM tb_login WHERE lg_useronline = 1";
    $query = mysql_query($sql) or die ("Errore nella query: " . mysql_error());
    $html = "";
    while($result = mysql_fetch_assoc($query)){
        html .= $result['lg_usr'] . ", ";
        }
     $html = substr($html,0,strlen($html)-2);
     echo $html;    
}