Notice php ครับ "Use of undefined constant assumed " เป็นเพราะอะไรหรอครับ

<?php
error_reporting(0);
define("MYSQL_NAME", "localhost");
define("MYSQL_USER", "root");
define("MYSQL_PASS", "");
define("MYSQL_DB", "samut");
?>

<?php
function con_db()  
{	

	$sql = mysql_connect(MYSQL_NAME,MYSQL_USER,MYSQL_PASS) or die(mysql_error() . ' : Line is ' . __LINE__ . ' File is ' . __FILE__);
	mysql_select_db(MYSQL_DB);
	if(defined('MYSQL_CHARSET')) 
	{
		mysql_query("SET NAMES '".MYSQL_CHARSET."'");
	}
	return $sql;
}
?>

<?php
require_once("config.php");         //require_once("backend/include/config.php"); 
require_once("function.php");      //require_once("backend/include/function.php"); 

$conn1 = con_db();
?>