【求助】C#中对数据库某一列的一个值进行更新的代码

这是这部分的代码，主要是想通过确认收货发货后，数据库的的表的那个值能相应的减少
using System;
using System.Data;
using System.Configuration;
using System.Collections;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Web.UI.HtmlControls;
using System.Data.SqlClient;

public partial class Manger_OrderModify : System.Web.UI.Page
{
MangerClass mcObj = new MangerClass();
UserInfoClass uiObj = new UserInfoClass();
public static CommonProperty order = new CommonProperty();
protected void Page_Load(object sender, EventArgs e)
{
if (Convert.ToString(Session["AID"]) == "")
{
Response.Redirect("Fail.aspx");
}
order = GetOrderInfo();
if (!IsPostBack)
{
rpBind();
IsCPCPBind();
}

}
public void IsCPCPBind()
{
    DataSet ds = mcObj.GetOdIfDS(Convert.ToInt32(Request["OrderID"].Trim()), "OrderInfo");
    chkConfirm.Checked = Convert.ToBoolean(ds.Tables["OrderInfo"].Rows[0][10].ToString());
    chkPay.Checked = Convert.ToBoolean(ds.Tables["OrderInfo"].Rows[0][11].ToString());
    chkConsignment.Checked = Convert.ToBoolean(ds.Tables["OrderInfo"].Rows[0][12].ToString());
    chkPigeonhole.Checked = Convert.ToBoolean(ds.Tables["OrderInfo"].Rows[0][13].ToString());

}
public void rpBind()
{
    DataSet ds=mcObj.GetGIByOID(Convert.ToInt32(Request["OrderID"].Trim()), "BookInfo");
    rptOrderItems.DataSource = ds.Tables["BookInfo"].DefaultView;
    rptOrderItems.DataBind();
}
/// <summary>
/// 获取指定订单信息
/// </summary>
/// <returns>返回CommonProperty类的实例对像</returns>
public CommonProperty GetOrderInfo()
{

    DataSet ds = mcObj.GetOdIfDS(Convert.ToInt32(Request["OrderID"].Trim()), "OrderInfo");
    DataSet UIDs = uiObj.ReturnUIDsByID(Convert.ToInt32(ds.Tables["OrderInfo"].Rows[0][7].ToString()), "UserInfo");
    order.OrderNo = Convert.ToInt32(ds.Tables["OrderInfo"].Rows[0][0].ToString());
    order.OrderTime = Convert.ToDateTime(ds.Tables["OrderInfo"].Rows[0][1].ToString());
    order.ProductPrice = float.Parse (ds.Tables["OrderInfo"].Rows[0][2].ToString());
    order.TotalPrice = float.Parse (ds.Tables["OrderInfo"].Rows[0][3].ToString());
    order.ShipPrice = float.Parse (ds.Tables["OrderInfo"].Rows[0][4].ToString());
    order.ReceiverName=ds.Tables["OrderInfo"].Rows[0][8].ToString();
    order.ReceiverPhone =ds.Tables["OrderInfo"].Rows[0][9].ToString();
    order.ReceiverPostalcode=ds.Tables["OrderInfo"].Rows[0][14].ToString();
    order.ReceiverAddress =ds.Tables["OrderInfo"].Rows[0][15].ToString();
    order.ReceiverEmail =ds.Tables["OrderInfo"].Rows[0][16].ToString();
    order.ShipType = Convert.ToInt32(ds.Tables["OrderInfo"].Rows[0][5].ToString());
    order.PayType = Convert.ToInt32(ds.Tables["OrderInfo"].Rows[0][6].ToString());
    order.BuyerAddress = UIDs.Tables["UserInfo"].Rows[0][9].ToString();
    order.BuyerEmail = UIDs.Tables["UserInfo"].Rows[0][8].ToString();
    order.BuyerName = UIDs.Tables["UserInfo"].Rows[0][1].ToString();
    order.BuyerPhone = UIDs.Tables["UserInfo"].Rows[0][7].ToString();
    order.BuyerPostalcode = UIDs.Tables["UserInfo"].Rows[0][11].ToString();

    return (order);


}
public string GetShippingName(int P_Int_ShipType)
{
    return mcObj.GetShipWay(P_Int_ShipType);

}
public string GetPaymentName(int P_Int_PayType)
{
    return mcObj.GetPayWay(P_Int_PayType);
}
public string GetStatus(int P_Int_OrderID)
{
    DataSet ds = mcObj.GetStatusDS(P_Int_OrderID, "OrderInfo");
    return (ds.Tables["OrderInfo"].Rows[0][0].ToString() + "|" + ds.Tables["OrderInfo"].Rows[0][1].ToString() + "<Br>" + ds.Tables["OrderInfo"].Rows[0][2].ToString() + "|" + ds.Tables["OrderInfo"].Rows[0][3].ToString());
}

protected void btnSave_Click(object sender, EventArgs e)
{
    bool IsConfirm;
    bool IsPayment;
    bool IsConsignment;
    bool IsPigeonhole;
    if (chkConfirm.Checked ==true )
    {
        IsConfirm = true;
    }
    else
    {
        IsConfirm = false;
    }
    if (chkPay.Checked ==true)
    {
        IsPayment = true;
    }
    else
    {
        IsPayment = false;
    }
    if (chkConsignment.Checked==true)
    {
        IsConsignment = true;
    }
    else
    {
        IsConsignment = false;
    }
    if(chkPigeonhole.Checked ==true)
    {
        IsPigeonhole = true;
    }
    else
    {
        IsPigeonhole = false;
    }



    mcObj.UpdateOI(Convert.ToInt32(Request["OrderID"].Trim()), IsConfirm, IsPayment, IsConsignment, IsPigeonhole);
    Response.Write("<script>alert('修改成功！')</script>");
    return;
}

}

这是我的数据库，我想更新的是这里面最后那个Inventory的值

先给你的表增加一个主键，也就是id，用来区别唯一的一行，而不是用什么最后一行、修改的一行之类模糊的说法。
sql

update 表 set 字段=值 where id=要修改的id