/e
<?php
session_start();
mysql_connect('localhost', 'root', 'password');
mysql_select_db('database');
if(isset($_SESSION['username'])) { header("Location: SEITE.php"); }
if(isset($_POST['submit'])) {
$Username = mysql_real_escape_string($_POST['username']);
$Password = md5($_POST['password']);
$CheckAccount = mysql_query("SELECT id FROM users WHERE username = '$Username' AND password = '$Password' LIMIT 1");
if(mysql_num_rows($CheckAccount)) {
$_SESSION['username'] = $Username;
header("Location: SEITE.php");
} else { echo "Falsche Zugangsdaten!"; }
}
?>
<!DOCTYPE html>
<html>
<head>
<title>Login</title>
</head>
<body>
<form method="POST">
Benutzername: <input type="text" name="username" />
Passwort: <input type="password" name="password" />
<input type="submit" name="submit" value="Einloggen" />
</form>
</body>
</html>