<?php
$dbhost = "localhost";
$dbname = "Datenbank Name";
$dbuser = "Datenbank Benutzername";
$dbpass = "Datenbank Passwort";
$user = $_GET['username'];
mysql_connect($dbhost, $dbuser, $dbpass)or die("Could not connect: ".mysql_error());
$verb = mysql_select_db($dbname);
if ($verb)
{
    $sql = "SELECT username FROM accountinformationen";
    $quer = mysql_query($sql) or die(mysql_error());
    $num = mysql_num_rows($quer);
    echo = $row;
}