php中的登陆login

<?php 
require "../include/DBClass.php"; 
$username=$_POST['UserName']; 
$password=$_POST['Password']; 
if(empty($username) || empty($password)){ 
  Go_Msg("请填写用户名，密码！","../default.html"); 
  exit; 
 } 
DBConn(); 
$password=md5($password); 
$SQL = "Select UserName,UserType,UserPass From siteuser where UserName='" . $username ."' and UserPass='" . $password . "' and isopen=1"; 
//echo "$SQL"; 
$result = $db -> exec_SQL($SQL); 
 $total=mysql_num_rows($result); 
 if($total==0){ 
  DBClose(); 
  Go_Msg("注册用户还没有通过管理员审核或用户名及密码不符！请重新输入！","../default.html"); 
  exit; 
 }else{ 
  $Rs = $db -> fetch_array($result); 
  //附值，并登录 
  session_register("username"); 
  session_register("usertype"); 
  $_SESSION["usertype"]=$Rs['UserType']; 
  $_SESSION["username"]=$username; 
  //echo $_SESSION["username"]; 
  if ($_SESSION["usertype"]==1){ 
    Go_Msg("登陆成功！","default.php"); 

    //header('Location:http://163.com'); 
  } 
  if ($_SESSION["usertype"]==2){ 
     Go_Msg("登陆成功！","../user2/default_1.php"); 
  } 
  if ($_SESSION["usertype"]==3){ 

     Go_Msg("登陆成功！","../user3/default_2.php"); 
  } 
  // header('Location:default.php'); 
 } 
DBClose(); 
// 何问起 hovertree.com
?>