if(table.getSelectionModel().getSelectedItems().iterator().hasNext()) {
                    db.insertOrder(new Bestellung(customerid,table.getSelectionModel().getSelectedItems().iterator().next()));

String ct = "CREATE TABLE Order (" + "Order_Id integer generated always as identity, " + "CUSTOMER_ID BIGINT" + "ISBN, CHAR(13) " + "PRIMARY KEY(Order_Id))";

String i = "INSERT INTO ORDER(CUSTOMER_ID,ISBN), VALUES(?,?)";
    Connection conn = null;
    PreparedStatement stmt = null;
    try {
        conn = DriverManager.getConnection(connString);
        stmt = conn.prepareStatement(i);
        conn.createStatement(ResultSet.TYPE_SCROLL_SENSITIVE,ResultSet.CONCUR_UPDATABLE);
        stmt.setLong(1, order.getCustomerId());
        stmt.setString(2, order.getBuch().getISBN());
        stmt.executeUpdate();
    } catch (SQLException e) {
        System.out.println(e.getMessage());
        e.printStackTrace();
    }
    finally {

        try {
            if (stmt != null)
                stmt.close();
            if (conn != null)
                conn.close();
        } catch (SQLException e) {
            System.out.println(e.getMessage());
            e.printStackTrace();
        }
    }

INSERT INTO ORDER(CUSTOMER_ID,ISBN), VALUES(?,?)
                                   ^

... + "ISBN, CHAR(13) " + ...
           ^