Classic asp SUM() retrieve wrong data type

in the following example the sum field get a wrong data type and script go in error

<%
set conn = server.CreateObject("ADODB.Connection")
conn_string = "DRIVER=

;port=3306;SERVER=127.0.0.1;UID=user;PWD=pwd;database=unit_test;charset=UTF8"
conn.open (conn_string)

set RS = server.CreateObject("ADODB.Recordset")
SQL = "SELECT number, SUM(number) AS total FROM testnumeric ORDER BY number"
RS.open SQL, Conn

Response.Write "work: "& RS("number") &"<br>"
sum = RS("number") + 1
Response.Write "work: "& sum &"<br>"

sum_number = RS("total") + 1 '<------ ERROR HERE
Response.Write "not work:"& sum_number

RS.close
set RS = Nothing

conn.close
set conn = Nothing

%>

can be avoided using Cint(RS("total"))

the table structure is
– --------------------------------------------------------
– Host: 127.0.0.1
– Versione server: 10.11.2-MariaDB - mariadb.org binary distribution
– S.O. server: Win64
– HeidiSQL Versione: 12.5.0.6677
– --------------------------------------------------------

/*!40101 SET @OLD_CHARACTER_SET_CLIENT=@@CHARACTER_SET_CLIENT */;
/*!40101 SET NAMES utf8 */;
/*!50503 SET NAMES utf8mb4 */;
/*!40103 SET @OLD_TIME_ZONE=@@TIME_ZONE */;
/*!40103 SET TIME_ZONE='+00:00' */;
/*!40014 SET @OLD_FOREIGN_KEY_CHECKS=@@FOREIGN_KEY_CHECKS, FOREIGN_KEY_CHECKS=0 */;
/*!40101 SET @OLD_SQL_MODE=@@SQL_MODE, SQL_MODE='NO_AUTO_VALUE_ON_ZERO' */;
/*!40111 SET @OLD_SQL_NOTES=@@SQL_NOTES, SQL_NOTES=0 */;

– Dump della struttura di tabella unit_test.testnumeric
CREATE TABLE IF NOT EXISTS `testnumeric` (
`number` int(11) DEFAULT NULL
) ENGINE=InnoDB DEFAULT CHARSET=latin1 COLLATE=latin1_swedish_ci;

– Dump dei dati della tabella unit_test.testnumeric: ~6 rows (circa)
INSERT INTO `testnumeric` (`number`) VALUES
(1),
(2),
(3),
(4),
(5),
(6);

/*!40103 SET TIME_ZONE=IFNULL(@OLD_TIME_ZONE, 'system') */;
/*!40101 SET SQL_MODE=IFNULL(@OLD_SQL_MODE, '') */;
/*!40014 SET FOREIGN_KEY_CHECKS=IFNULL(@OLD_FOREIGN_KEY_CHECKS, 1) */;
/*!40101 SET CHARACTER_SET_CLIENT=@OLD_CHARACTER_SET_CLIENT */;
/*!40111 SET SQL_NOTES=IFNULL(@OLD_SQL_NOTES, 1) */;