ช่วยเขียนโค้ด ระบบ login การใช้งาน แบ่งตามชนิดของผู้ใช้งาน

<?
session_start();
$username = $_POST["username"];
$password = $_POST["password"];

include 'connect.php';
$sert = "insert into monitor values('$username','$date','$time')";
mysql_query($sert) or mysql_errno();

$chk2= mysql_query("select servname,password
            from server
            where servname='$username'and password ='$password'");
        $rows_num = mysql_num_rows($chk2);

        if($rows_num>0 )
            {
               $rowchk = mysql_fetch_array($chk2);
        $_SESSION['username'] = "$username";
        $_SESSION['password'] ="$password";
        {
            header("Location:user_main.php");
        }

    }

else  ($chk= mysql_query("select account,password
            from login
                    where account='$username'and password ='$password'"));
{
        $rows_num = mysql_num_rows($chk);
    if($rows_num>0 ) {
       $rowchk = mysql_fetch_array($chk);
        $_SESSION['username'] = "$username";
        $_SESSION['password'] ="$password";
        {
            header("Location:admin_main.php");
        }

    }

else
     header("Location:logout.php");
     }

     ?>

$sql = "select username, password, type from member where username = '$username' and password = '$password'";
$result = mysql_query($sql);
$rows = mysql_fetch_array($result);
	$user = $rows["username"];
	$type = $rows["type"];
	if(isset($user)) //พบ username
	{
		$_SESSION["user"] = $user;
		$_SESSION["type"] = $type;
	}
	else
	{
	        echo "Error";
	}