php mysql สอบถามเกี่ยวกับการใช้ SESSION กับการตรวตสอบค่าการ login คับ

<?
session_start();
$Username=$_POST['Username'];
$Password=$_POST['Password'];
$Select=mysql_query("SELECT * FROM tb_member WHERE Username='".$Username."' AND Password='".$Password."'") or die (mysql_error());
$Num_Rows=mysql_num_rows($Select);

if($Num_Rows != 0){
    $_SESSION['Username']=$Username
   header("location:index.php");
}else{
   echo " Login ไม่สำเร็จ";
}

<?
	session_start();
	mysql_connect("localhost","root","root");
	mysql_select_db("mydatabase");
	$strSQL = "SELECT * FROM member WHERE Username = '".trim($_POST['txtUsername'])."' 
	and Password = '".trim($_POST['txtPassword'])."'";
	$objQuery = mysql_query($strSQL);
	$objResult = mysql_fetch_array($objQuery);
	if(!$objResult)
	{
			echo "Username and Password Incorrect!";
	}
	else
	{
			$_SESSION["UserID"] = $objResult["UserID"];
			$_SESSION["Status"] = $objResult["Status"];

			session_write_close();
			
			if($objResult["Status"] == "ADMIN")
			{
				header("location:admin_page.php");
			}
			else
			{
				header("location:user_page.php");
			}
	}
	mysql_close();
?>

session_start();
if($_SESSION['Username'] == ""){
    //*สร้างฟอร์ม login
}else{
   echo $_SESSION['Username'];
}