asp.net中DataSet的问题

MySQLConnection conn = new MySQLConnection(new MySQLConnectionString("192.168.0.56", "antshop", "root", "qwe123").AsString);
            conn.Open();
string sql = "SELECT a.salesman,SUM(b.qty/b.qtyOfPackage),b.expiryDate FROM saleorderbill a,saleorderbilldetail b,brand c,goods d WHERE a.billCode=b.billCode AND b.goods_id=d.id AND d.brand_id=c.id AND b.money<>0 AND a.salesman='刘俊斌' GROUP BY a.salesman,c.`name`,b.expiryDate";
            MySQLCommand comm = new MySQLCommand(sql, conn);
            comm.ExecuteNonQuery();
            MySQLDataAdapter da = new MySQLDataAdapter();
            da.SelectCommand = comm;
            DataSet ds = new DataSet();
            da.Fill(ds);