ทำ Login โดยมีฐานข้อมูล 3 ฐานข้อมูลอ่ะคะ จะเขียนยังไงอ่ะ โดยที่ไม่แบ่ง เลเวล อ่ะ

<?
	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();
?>

$sql = "select members.* from  
( 
select username, `password`, 3 as `user_type` from `member`  
union  
select `user` as username, `password`, 2 as `user_type` from `admin_member` 
union  
select `name` as username, `password`, 1 as `user_type` from `engineer` 

) 
as members 
where username = '" . $username . "' and `password` = '" . $password . "'";