//指定資料庫列求和
        public string zhidinglieqiuhe(string sql)
        {
            SqlConnection conn = DB.lianjie();
            conn.Open();
            SqlCommand cmd = new SqlCommand(sql, conn);
            SqlDataReader myr = cmd.ExecuteReader();
            myr.Read();
            string sum = myr.GetValue(0).ToString();
            return sum;
        }