Java 如何合并JTable和MySql中同名表中的行

Java代码

 ResultSet rs=null;
        String sqlquery="";
        Statement st;
        String var="";

        double sum = 0;

    try{
        Class.forName("com.mysql.jdbc.Driver");
        conn = DriverManager.getConnection("jdbc:mysql://localhost/mypos","root","");
        Statement stmt=(Statement)conn.createStatement();


        String prod = fld_product.getText();
        int quant = Integer.parseInt(fld_quantity.getText());
        float price = Float.parseFloat(fld_price.getText());
        String query = "INSERT INTO Cart (Product, Quantity, Price) VALUES ('"+prod+"','"+quant+"','"+price+"');";
        stmt.executeUpdate(query);

        while(rs.next()){
            String product = rs.getString("Product");
            sum = Integer.parseInt(rs.getString("quantity")) + quant;

            if(prod.equals(product)){
                String sql2 = "UPDATE Product SET quantity = "+sum+" WHERE product = '"+prod+"'";
                stmt.executeUpdate(sql2);
            } else{
                String sql1 = "INSERT INTO Product (product,quantity,price) " + "VALUES ('"+prod+"', '"+quant+"', '"+price+"')";
                stmt.executeUpdate(sql1);
            }
        }
        conn.close();
        JOptionPane.showMessageDialog(null, "PRODUCT SAVED!","SUCCESS", JOptionPane.PLAIN_MESSAGE);
    }catch(Exception e){
        JOptionPane.showMessageDialog(null, e.getMessage() ,"ERROR!", 1);
    }
        this.loadCartToJTable();
        this.clearFields();
}  

我不知道发生了什么事。当我输入coke作为产品时，它会打印价格，但当我输入相同的产品coke时，行会合并，但价格和数量总是会被覆盖