玩下datatable~~哈哈!

        public static DataTable mydt(DataTable dt, DataTable dt2) {
            DataColumn dc = new DataColumn();
            dt.Columns.Add("dd");
            for (int i = 0; i != dt.Rows.Count; i++) {
                dt.Rows[i]["dd"] = mydt2(dt2, dt.Rows[i]["type_id"].ToString());
            }
            return dt;
        }
        public static string mydt2(DataTable dt,string where_value) {
            for (int i = 0; i != dt.Rows.Count; i++) {
                if (dt.Rows[i]["type_id"].ToString() == where_value) {
                    return dt.Rows[i]["type_name"].ToString();
                }
            }
            return "";
        }
        public void abc() {
            DropDownList myddl = new DropDownList();
            DataTable dt1 = new DataTable();
            DataTable dt2 = new DataTable();
            myddl.DataSource = mydt(dt1, dt2);
            myddl.DataBind();
        }