pst=conn.prepareStatement(sql);
            pst.setString(1,txt_firstname.getText());
            pst.setString(2,txt_surname.getText());
            pst.setString(3, txt_fee.getText());
            pst.setString(4, (String) cbox_time.getSelectedItem());
            pst.setString(5,txt_date.getText());
            pst.setString(6, (String) cbox_doctors.getSelectedItem());
            pst.executeUpdate();