Based Email or Username

if(isset($_POST['process']) && ($_POST['username'] !='') & ($_POST['password']!='')){

        $username = cleaninput ($_POST['username']);
        $password = cleaninput(md5($_POST['password']));
        $check_email = Is_email($username);

    $query = $connect->prepare("SELECT * FROM users WHERE username = ? AND password = ?");

    if($check_email){
                        $query = $connect->prepare("SELECT * FROM users WHERE email = ? AND password = ?");
    }

        $query->bind_param('ss', $username, $password);

        $query->execute();
        $query->bind_result($id_user, $username, $password, $nama_depan, $nama_belakang, $alamat, $email, $idlevel, $no_kontak, $jenis_kelamin, $foto);
        $query->store_result();
        $nums = $query->num_rows;
        $query->fetch();

        if($nums > 0){

                $_SESSION['id_user'] = $id_user;
                $_SESSION['username'] =$username;
                $_SESSION['nama_depan'] = $nama_depan;
                $_SESSION['nama_belakang'] = $nama_belakang;
                $_SESSION['email'] = $email;
                $_SESSION['idlevel'] = $idlevel;

                        switch($_SESSION['idlevel']){
                        case 1 :
                        header('location:admin/index.php');
                        break;
                        case 2 :
                        header('location:staff/index.php');
                        break;
                        case 3 :
                        header('location:marketing/index.php');
                        break;
                        }
        }else{
                header('location:index.php');
        }

} else{
                header('location:index.php');
}