ขอสอบถามเกี่ยวกับเรื่อง PHP OOP หน่อยครับ พอดีมีปัญหาเรื่องการ Query ข้อมูลครับ

<?
/* Connect Database */
$db1=new db;
$db1->open();
$db1->setContent("utf8");

/* Select Table */
$sql_category = "select * from "._TB_1_." where c_sub='0'";
$qry_category = $db1->query($sql_category);


/* Select Table */
$sql_product_status = "select * from "._TB_2_."";
$qry_product_status = $db1->query($sql_product_status);

/* Close Database */
$db1->close();


?>

<?

class DB

{

    // Connection parameters

	var $host = 'localhost';
        var $user ="root";
        var $password ="1234";
        var $persistent = false;
	var $adminid='';
	var $adminipwd='';
	var $database = 'test';

	// Database connection handle

    var $conn = NULL;
    var $result = false;   // Query result

	function setContent($type)
	{
		$cs1 = "SET character_set_results=".$type;
		mysql_query($cs1) or die('Error query: ' . mysql_error()); 
		$cs2 = "SET character_set_client =".$type;
		mysql_query($cs2) or die('Error query: ' . mysql_error()); 
		$cs3 = "SET character_set_connection =".$type;
		mysql_query($cs3) or die('Error query: ' . mysql_error());
	}
	
    function open()

    {
        // Choose the appropriate connect function
        if ($this->persistent) {
            $func = 'mysql_pconnect';
        } else {
            $func = 'mysql_connect';
        }

        // Connect to the MySQL server
        $this->conn = $func($this->host, $this->user, $this->password);
        if (!$this->conn) {
            return false;
        }

        // Select the requested database
        if (!@mysql_select_db($this->database, $this->conn)) {
			echo "Database is wrong!!!";
            return false;
        }
		
        return true;

    }

    function close()
    {
        return (@mysql_close($this->conn));
    }

    function query($sql = '')

    {
        $this->result = @mysql_query($sql, $this->conn);
		return ($this->result != false);
    }

    function fetchAssoc()
    {

        return (@mysql_fetch_assoc($this->result));
    }
?>

<?
/* Connect Database */
$db1=new db;
$db1->open();
$db1->setContent("utf8");

/* Select Table */
$sql_category = "select * from "._TB_1_." where c_sub='0'";
$qry_category = $db1->query($sql_category);

/* Close Database */
$db1->close();



/* Connect Database */
$db2=new db;
$db2->open();
$db2->setContent("utf8");

/* Select Table */
$sql_product_status = "select * from "._TB_2_."";
$qry_product_status = $db2->query($sql_product_status);

/* Close Database */
$db2->close();


?>