protected void Page_Load(object sender, EventArgs e)
        {
            if (!IsPostBack)
            {
                dtKhachHang dt1 = new dtKhachHang();
                DataTable   da1 = dt1.LayDanhSachKhachHang_InBaoCao();
                da1.Rows.Add(-1, "Tất cả khách hàng");

                ccbKhachHang.DataSource = da1;
                ccbKhachHang.TextField  = "TenKhachHang";
                ccbKhachHang.ValueField = "ID";
                ccbKhachHang.DataBind();
                ccbKhachHang.SelectedIndex = da1.Rows.Count;
            }
        }