PHP 5.2.14 session register

session_unset();
/**
 * @Nexen 
 * @copyright 2012
 */

 require("conf.php");
 


/** register */ 
$con = mysql_connect("127.0.0.1","x","x");
if (!$con)
  {
     die('Could not connect!');
  }
mysql_select_db("x", $con);

/** definition */
$postusername = mysql_real_escape_string($_POST['username']);
$postpassword = mysql_real_escape_string($_POST['password']);
$button = mysql_real_escape_string($_POST['login']);


if(isset($_POST['login']) && $postpassword && $postusername){
    
            $sha_pass = sha1(strtoupper($postusername.':'.$postpassword));
            $encrypt = $sha_pass;
            
                $query = "SELECT * FROM `account` WHERE `username`='" . mysql_real_escape_string($postusername) ."' AND `sha_pass_hash`='".mysql_real_escape_string($encrypt)."'";
                $result = mysql_query($query) or die('MySQL error, retry!');
                if(mysql_num_rows($result)) 
                {
                      session_start(); 
                        session_register('username'); 
                     
                    echo "<script>alert('Přihlášení proběhlo úspěšně!')</script>";
                    echo "<script type='text/javascript'>
                    <!--
                        window.location = 'x/index.php'
                    //-->
                  </script>";
                }
                else
                {
                        session_destroy();
                        echo "<script>alert('Nelze se přihlásit, jste zaregistrovaný?')</script>";
                    echo "<script type='text/javascript'>
                    <!--
                        window.location = 'x/index.php?page=register'
                    //-->
                  </script>";
                    
                }
            


}