$(document).ready(function() {

  $("form#login_form").submit(function() {  

     var login_username     = $('#login_username').attr('value');  
     var login_password     = $('#login_password').attr('value');  
        type: "POST",  
         $.ajax({  
            url: "login.php",  
            data: "username="+ login_username +"& password="+ login_password,  
            success: function(data){
                alert(data);
                if (data == "ok"){  
                     $('form#login_form').hide(function(){$('div.success').fadeIn();});  
                    }
               }
         });  
     return false;  
     });

Login.php:

<?php
    include("settings.php");
    $query = "select * from users where username = '{$_POST['login_username']}' and password = md5('{$_POST['login_password']}')";  
    $query = mysql_query($query, $connection);
        if ( mysql_num_rows($query) == 1 )
        {       
            print "ok";
            $array = mysql_fetch_array($query);
            if ( $_POST['stay'] ) { $time = time()+2592000; }
            else { $time = 0; } 
        }
        else {  print "no"; }
        mysql_close($connection);
    ?>

My problem: In the alert the message always "no" whether username/password is correct, however on the site "ok" appears when username/pw is correct.

I have read the other questions in connection with this problem, but I couldn't solve the response problem from login.php with Json. Could you help me how should I response to the ajax calling? ( with a code if it is possible) Thank you very much, and sorry for questioning again.