this.DBConnect();
            this.OpenConnect();

            string querry = "INSERT INTO Orders( OrdersClientsName, OrdersDate,OrdersDriverName, OrdersCarModel, OrdersCarKey, OrdersTotalPrice)" + "VALUES('"+ ClientsName + "','" + Date + "','" + Driver +"','"+CarModel+"','"+CarKey+"','"+TotalPrice+"');"; //добавление данных в OrdersID
            this.cmd = new MySqlCommand(querry, this.connection);
            this.cmd.ExecuteNonQuery();
            this.CloseConnect();

            this.DBConnect();
            this.OpenConnect();
            for (int i = 0; i < dt.RowCount - 1; i++)
            {
                double price = Convert.ToDouble(dt.Rows[i].Cells[1].Value.ToString());
                int count = Convert.ToInt32(dt.Rows[i].Cells[2].Value.ToString());
                double goods_total_price = Convert.ToDouble(dt.Rows[i].Cells[3].Value.ToString());
                querry = "INSERT INTO OrdersGoodsDetails(OrdersGoodsDetails_GoodsName, OrdersGoodsDetails_GoodsPrice,OrdersGoodsDetails_GoodsCount, OrdersGoodsDetails_GoodsTotalPrice)" + "VALUES('" + dt.Rows[i].Cells[0].Value.ToString() + "','" + price + "','" + count + "','" + goods_total_price + "');"; //добавление выбранного товара из datagridview в таблицу OrdersGoodsDetails
                this.cmd = new MySqlCommand(querry, this.connection);
                this.cmd.ExecuteNonQuery();//здесь вылетает ошибка
            }
            this.CloseConnect();

CREATE TABLE IF NOT EXISTS `orders` (
  `OrdersID` int(11) NOT NULL AUTO_INCREMENT,
  `OrdersClientsName` varchar(15) NOT NULL,
  `OrdersDate` varchar(20) NOT NULL,
  `OrdersDriverName` varchar(20) NOT NULL,
  `OrdersCarModel` varchar(20) NOT NULL,
  `OrdersCarKey` varchar(10) NOT NULL,
  `OrdersTotalPrice` double NOT NULL,
  PRIMARY KEY (`OrdersID`),
  KEY `DriverID` (`OrdersDriverName`)
) ENGINE=InnoDB  DEFAULT CHARSET=utf8 AUTO_INCREMENT=5 ;

CREATE TABLE IF NOT EXISTS `ordersgoodsdetails` (
  `OrdersGoodsDetailsID` int(11) NOT NULL AUTO_INCREMENT,
  `OrdersID` int(11) NOT NULL,
  `OrdersGoodsDetails_GoodsName` varchar(15) NOT NULL,
  `OrdersGoodsDetails_GoodsPrice` double NOT NULL,
  `OrdersGoodsDetails_GoodsCount` int(11) NOT NULL,
  `OrdersGoodsDetails_GoodsTotalPrice` double NOT NULL,
  PRIMARY KEY (`OrdersGoodsDetailsID`),
  KEY `OrdersID` (`OrdersID`)
) ENGINE=InnoDB  DEFAULT CHARSET=utf8 AUTO_INCREMENT=6 ;

--
-- Ограничения внешнего ключа сохраненных таблиц
--

--
-- Ограничения внешнего ключа таблицы `ordersgoodsdetails`
--
ALTER TABLE `ordersgoodsdetails`
  ADD CONSTRAINT `ordersgoodsdetails_ibfk_1` FOREIGN KEY (`OrdersID`) REFERENCES `orders` (`OrdersID`);