не работает md5()

    $login = $_POST['login'];
    $pass = $_POST['pass'];
 
    $pass = md5($pass."gh12khgc3");
    $mysql = new mysqli("localhost", "root", "", "startbip");
 
    $result = $mysql->query("SELECT * FROM `user` WHERE `login` = '$login' AND `pass` = '$pass'");
 
    $user = $result->fetch_assoc();
 
    if (count($user) == 0) {
        header('Location: login.php');
    }
    else {
        setcookie('user', $user['name'], time() + 3600, "/");
        setcookie('user_surname', $user['surname'], time() + 3600, "/");
        header('Location: index.php');
    }
    $mysql->close();

    $name = filter_var(trim($_POST['name']), FILTER_SANITIZE_STRING);
    $surname = filter_var(trim($_POST['surname']), FILTER_SANITIZE_STRING);
    $middle = filter_var(trim($_POST['middle']), FILTER_SANITIZE_STRING);
    $login = filter_var(trim($_POST['login']), FILTER_SANITIZE_STRING);
    $pass = filter_var(trim($_POST['pass']), FILTER_SANITIZE_STRING);
    require_once "../assets/functions/function.php"; 
 
 
    // $pass = md5($pass."gh12khgc3");
 
    if (($name == '') or ($surname == '') or ($login == '') or ($pass == '')) {
    
 
    }
    else {
    connectDB();
    $mysqli->query("INSERT INTO `user` ( `name`, `surname`, `middle`,`login`,`pass` ) VALUES ('$name', '$surname', '$middle','$login', '$pass') ");
    $mysqli->close();
    header('Location: control.php');
}

md5($_POST['pass'] ."gh12khgc3");

filter_var(trim($_POST['pass']), FILTER_SANITIZE_STRING);