将值从gridview中的一列移动到同一gridview中的另一列

Question

ID      sum     payed
1       354     200       
1       2345    23435     

我有gridview2来自gridview1，其中选择的行checkbox。 我想将值从sum移动到payd，因此payed从sum中获取值，然后sum变为空。请帮助我，我是新手。 谢谢:)

namespace WebApplication5
{
 public partial class Presmetuvanje : System.Web.UI.Page
 {
    public int @UserID;
    SqlConnection sqlConn = new SqlConnection(Web.GetConfigValue("proekt1"));
    //private DataTable dt;

    protected void Page_Load(object sender, EventArgs e)
    {
        SqlConnection sqlConn = new SqlConnection(Web.GetConfigValue("proekt1"));


        if (Web.IsMemberSession)
        {
            Response.Write("Welcome" + " " + Web.SessionUser.Naziv);
        }

    }

    protected void Button2_Click(object sender, EventArgs e)
    {
        String Oznacheni = "";

        SqlConnection sqlConn = new SqlConnection(Web.GetConfigValue("proekt1"));
        CheckBox ch;

        foreach (GridViewRow row in GridView1.Rows)
        {
            ch = (CheckBox)row.FindControl("CheckBox1");
            if (ch.Checked == true)
            {
                String pom = row.Cells[0].Text;
                if (Oznacheni.Length > 0) pom = ", " + pom;
                Oznacheni += pom;
            }

        }

        if (Oznacheni.Length < 1) Oznacheni = "-1";
        SqlDataSource2.SelectCommand = " SELECT * FROM fakturis WHERE fakturaID IN (" + Oznacheni + ")";
        SqlDataSource2.DataBind();
        GridView2.DataBind();  


    }

 protected void Button1_Click(object sender, EventArgs e)
    {
        try
        {
            Web.SessionUser = null;
            Web.IsMemberSession = false;
            Response.Redirect("Login.aspx");
        }
        catch (Exception ex)
        {
            Response.Write(ex.Message);
        }
    }

 protected void Button3_Click(object sender, EventArgs e)
    {


        int sum = 0;
        for (int i = 0; i < GridView2.Rows.Count; i++)
        {
            sum += int.Parse(GridView2.Rows[i].Cells[7].Text);

        }
        Label1.Text = "Platenata suma iznesuva "+sum.ToString() +" denari";
   }


}
 }

在此Button3_Click之后，我想添加新方法，将值从sum添加到payd 然后总和变空了。