rules: {

        username: {
            required: true
        },
        password: {
            required: true
        }
    },
    messages: {
        //etc
    },
    submitHandler: function(form) {

        $.ajax({
            type: "POST",
            url: 'php/login.php',
            data: $('form').serialize(),

            success: function(data) {

                console.log(data);
                if (data === "1")
                {
                    console.log("username and password matched with database");
                } else
                {
                    console.log("invalid username or password");
                }
            }
        });
        return false;
    }
});

include 'php/database.php';

    $username = $_POST['username'];
    $password = $_POST['password'];

    $sql = "SELECT * FROM login WHERE username='$username' AND password='$password'";
    $result = $conn->query($sql);

    if ($result->num_rows > 0)
    {
        echo true;
    } else
    {
        echo false;
    }

<?php

    $username = $_POST['username'];
    $password = $_POST['password'];

    if($username === "bob" && $password === "123")
    {
        echo true;
    }else
    {
        echo false;
    }
?>