MySql does not return anything

I'm just messing around with PHP and MySql to learn things... Untill now everything worked out fine, but now I just can't find any solution. The base is a very simple login system. Now i was trying to read username and password from a database called 'login' with the table 'userTBL' and fields 'username' and 'password'.

 <?php
    session_start();

    mysql_connect ('localhost', 'root', 'root') or die('NO MYSQL CONNECTION!');
    mysql_select_db('login');  

    if ($_GET['login']) {
        $username = ($_POST['username']);
        $password = ($_POST['password']);

        $tmp = mysql_query("SELECT * FROM `user`");

        $data = mysql_fetch_array($tmp);

        if($tmp) {
            echo 'FULL<br />';
        } else {
            echo 'EMPTY<br />';
        }

        $_SESSION['username'] = $data['username'];
        $_SESSION['password'] = $data['password'];

         if ($username == $_SESSION['username'] && $password == $_SESSION['password']) {
             $_SESSION['loggedin'] = true;
             header("Location: protected.php");
             exit;
         } else echo "Wrong details!<br />";
    }
    if ($_SESSION['loggedin'] == true) {
        header("Location: protected.php");
    }
?>

It seems like the database would not return anything, but why?!?!

Thanks for your help!

---

You mentioned that your table is called 'userTBL' but you're querying the table 'user'. Change your query to this: $tmp = mysql_query("SELECT * FROM userTBL WHERE username = {$username} AND password = {$password}"); The 'WHERE' clause will ensure that the query only returns data matching the username and password that was typed into the form.