belajar session

/*******************/
FILE: login.php

<table width="429" border="0" align="center" cellpadding="0" cellspacing="0">
  <tr>
    <td width="429" height="15" bgcolor="#333333"><h3 align="center" class="style1">PORTAL SISTEM  AKADEMIKA </h3></td>
  </tr>
  <tr>
    <td height="162" bgcolor="#CCCCCC">
        <form action="proses.php" method="post">
          <div align="justify"></div>
          <table width="310" border="0" align="center" cellpadding="0" cellspacing="0">
            <tr>
              <td width="97"><span class="style4">Username </span></td>
              <td width="267">
                <input type="text"
                       name="username"
                       size="25"
                       placeholder="Masukan Username Anda" />
              </td>
            </tr>
            <tr>
              <td height="41"><span class="style4">Password </span></td>
              <td>
                 <input type="password"
                        name="password"
                        size="25"
                        placeholder="Masukan Password Anda"/>
              </td>
            </tr>
            <tr>
              <td>&nbsp;</td>
              <td><input type="submit" name="submit" value="LOGIN"></td>
            </tr>
          </table>
        </form>
    </td>
  </tr>
</table>

/*******************/
FILE: process.php

<?php
session_start(); //memulai session
include "konek.php";
$msg='';
// check submit
if(isset($_POST['submit']))
{
  //query untuk mengambil data user dari database sesuai dengan username inputan form
  $sql = "SELECT level,username
          FROM user
          WHERE username = '".$_POST['username']."' AND password='".$_POST['password']."'";
  if($result = mysql_query($sql))
  {
    if (mysql_num_rows($result)==1)
    {
      //menyimpan tipe user dan username dalam session
      $_SESSION['level'] = $data['level'];
      $_SESSION['username'] = $data['username'];
      //redirect halaman sesuai 'level'-nya
      header('location:'.$data['level'].'/home_'.$data['level'].'.php');
    }
    //jika password/username tidak sesuai
    else
    {
    $msg='Username / Password Salah atau tidak ditemukan';
    }
  }
  else
  {
    $msg='Terjadi kesalahan pada database';
  }
}
else
{
  $msg='Anda tidak berhak mengakses halaman ini langsung';
}
echo "<center><font color='red'>$msg</font><br><a href='index.php'>Kembali</a></center>";
?>

/*******************/
FILE: session.php
<?php
session_start();
if ($_SESSION['level'] == "admin")
{
  header('location:admin/home_admin.php');
}
elseif ($_SESSION['level'] == "user")
{
  header('location:user/home_user.php');
}
?>