met belajar

<?php
require_once("koneksi.php");

if(isset($_POST['username'])&&isset($_POST['password'])){
 if(isset($_POST['register'])){
    $username = $_POST['username'];
    $pass = $_POST['password'];
    $cekuser = mysql_query("SELECT * FROM user WHERE username = '$username'");
//------------------------
    if(mysql_num_rows($cekuser) <> 0) {
        echo "<script language=\"javascript\">
                    alert(\"Username Sudah Terdaftar\");
                </script>";
        break;
    }
    else {
        if(!$username || !$pass) {
            echo "<script language=\"javascript\">
                        alert(\"Ada Data Yang Kosong!\");
                    </script>";
            break;
        }
        else {
            $simpan = mysql_query("INSERT INTO user(username, password) VALUES('$username','$pass')");
            if($simpan) {
                echo "<script language=\"javascript\">
                            alert(\"Pendaftaran Sukses\");
                        </script>";
                break;
            }
            else {
                echo "<script language=\"javascript\">
                            alert(\"Proses Gagal\");
                        </script>";
                break;
            }
        }
    }
 }else{
    session_start();
    $username = $_POST['username'];
    $pass = $_POST['password'];
    $sql="SELECT count(username) total
        FROM user WHERE
        username = '$username'";
    $cekuser = mysql_query($sql);
    $row = mysql_fetch_array($cekuser);
    if($row['total'] == 0) {
        echo "<script language=\"javascript\">
                    alert(\"Username Belum Terdaftar\");
                </script>";

    }else{
        $sql="SELECT * total
        FROM user WHERE
        username = '$username'";
        $cekuser = mysql_query($sql);
        //$row = mysql_fetch_array($cekuser);
        $hasil = mysql_fetch_array($cekuser);
        if($pass != $hasil['password']) {
            echo "<script language=\"javascript\">
                        alert(\"Password Salah!\");
                    </script>";
            break;
        }
        else {
            $_SESSION['username'] = $hasil['username'];
            $_SESSION['level_user'] = $hasil['level_user'];
            //header('location:index.php');
/*
        carilah javascript gotourl.. jangan pake header.. trust me!!
*/
        }

    }
//  $jumlah = mysql_num_rows($cekuser);

 }

}else{}



?>