Rückgabeabfrage und noch einige fragen

PHP Code:
            $sql = "SELECT
                        tb_kunde_id
                    FROM
                        db_kunde
                    WHERE
                        tb_kunde_vorname = :vorname
                            AND
                                tb_kunde_nachname = :nachname
                            AND
                                tb_kunde_land = :land";
            $select = $db->prepare($sql);
            $select->bindParam(':vorname', $tb_kunde_vorname);
            $select->bindParam(':nachname', $tb_kunde_nachname);
            $select->execute();
            if($select->rowCount() < 1)
                {
                    $client_data['tb_kunde_vorname'] = $tb_kunde_vorname;
                    $client_data['tb_kunde_nachname'] = $tb_kunde_nachname;
                    $add_client = $db->insert("db_kunde",$client_data) OR die("Error: ".$db->error()."</br> Zeile ".__LINE__);
                    $id_kunde = $db->lastInsertId();
                }
            else
                {
                    $results = $select->fetch(PDO::FETCH_NUM);
                    $id_kunde = $results[0];
                }