inserting an extra column in grid view with already existed columns

i gave the description in solution window now can u pls help me

i explain in solution section on solution 3

SqlDataAdapter da=new SqlDataAdapter("select SNO,DATE,PNAME,QUANT,RATE,TOTAL from BILL1 where CNAME='"+Label1.Text+"' and DATE between '" + dt1.ToShortDateString() + "' and '" + dt2.ToShortDateString() + "'",con);
DataSet ds=new DataSet();
da.Fill(ds);
GridView1.DataSource = ds;
GridView1.DataBind();
con.Close();

/////////////
con.Open();
SqlCommand cmd = new SqlCommand("select SNO,DATE,PNAME,QUANT,RATE,TOTAL from BILL1 where CNAME='" + Label1.Text + "' and DATE between '" + dt1.ToShortDateString() + "' and '" + dt2.ToShortDateString() + "'", con);

SqlDataReader dr1 = cmd.ExecuteReader();
while (dr1.Read())
{


a += Convert.ToDecimal(dr1["TOTAL"].ToString());
// SqlConnection con1 = new SqlConnection(ConfigurationManager.ConnectionStrings["order"].ConnectionString);
// SqlCommand cmd1 = new SqlCommand("update BILL1 set BALANCE=" + a + "", con1);
// con1.Open();
// cmd1.ExecuteNonQuery();
// con1.Close();

}
Label5.Text = a.ToString();
Label6.Text = a.ToString();
con.Close();

}

protected void Button1_Click(object sender, EventArgs e)
{
Page.RegisterStartupScript("PrintPage", "<script language='javascript'>window.print()</script>");
}

protected void Button2_Click(object sender, EventArgs e)
{
Response.Redirect("GENERATEBILL2.aspx");
}