การล็อคอิน อยากถามพี่อะครับว่าเวลาเรา Login ไม่ผ่านให้มันโชว์ข้อความบอกแล้วค่อยรหัสผ่านหรือยูสเซอร์ไม่ถูกต้อง

<form name='login' action="check.php" method="post">

              <b><H1>LOG IN</H1></b>
             <br>
             Username :
             <input name='username' type='text' id='username' value="<? echo "$username"; ?>" maxlength='15' />
             <br>
           Password :
             <input type='password' name='password' id='password' maxlength='15'/>
              <br>
	           <input type='submit' name='submit' id='submit' value='login'  />
 
			   <? echo "$code_error"; ?>

session_start();

$server = "localhost"; // mySQL Server, most cases "localhost" 
$db_user = "root"; // mySQL Username 
$db_pass = ""; // mySQL Password 
$dbname = "myDB"; // Database Name
$tablename = "login"; //Table name
mysql_connect($server,$db_user,$db_pass)or die("Can't connect to Database?") ;
mysql_select_db($dbname)or die("Can't select Database");

$sql = "select * from $tablename where username='".$_POST["username"]."' AND password='".$_POST["password"]."'";
$dbquery =mysql_db_query($dbname,$sql);
$num_rows = mysql_num_rows($dbquery);


if($num_rows==0) // check whether there's no row effected by SQL command
{
	$code_error="Your username or password is incorrect  Try to login again";
	session_register("code_error");
	session_register("username");
	header("location:login.php"); 
}
else
{
               session_register("username");
               header("localtion:user.php");
}