<form action="login_controller.php" method="POST">
        <span class="user_label">Username: </span>
        <input class="username" type="text" name="username"><p>
        <span class="pass_label">Password: </span>
        <input class="password" type="password" name="password"><p>
        <input class="submit" type="submit" name="submit" value="Login">
</form>

<?php
    require_once 'config/config.php';

if (isset($_POST['submit']) && $_POST['submit'] == 'Login') {

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

    if (!empty($username) && !empty($password)) {


        $users_count = $pdo->query("SELECT COUNT(username)
                                    FROM users
                                    WHERE username = {$username}");
        $count_all = $users_count->fetchColumn();

        print_r($count_all);

    }

    else {
        header('Location: login.php');
    }

}