$sql8921 = mysql_query("SELECT count(id) FROM users WHERE online > NOW() - interval 20 minute") or die(mysql_error());
if(mysql_num_rows($sql8921) > 0){
                   $rows8921 = mysql_fetch_array($sql8921);
echo $rows8921['count(id)'];
} else {


echo "Er zijn geen gebruikers online!";


}