สอนถามเรื่องการใช้งาน OOP กับการ WHILE หน่อยครับ เขียน CLASS ใช้งานครับ

$db1=new db;
$db1->open();
$db1->setContent("utf8");
$sql_cat = "SELECT * FROM category";
$db1->query($sql_cat);

while($arr_cat = $db1->fetchAssoc())
	{

		echo "<ul>".$arr_cat['cname'];
		echo $sql_subcat = "SELECT * FROM subcategory where cid=".$arr_cat['cid']."";
		$db1->query($sql_subcat);
			while($arr_subcat = $db1->fetchAssoc())
				{
					echo "<li>".$arr_subcat['subname']."</li>";
				}
		echo "</ul>";
	}

while($arr_cat = $db1->fetchAssoc())
	{

		echo "<ul>".$arr_cat['cname'];
		echo $sql_subcat = "SELECT * FROM subcategory where cid=".$arr_cat['cid']."";
		$db2=new db;
		$db2->open();
		$db2->setContent("utf8");
		$db2->query($sql_subcat);
			while($arr_subcat = $db2->fetchAssoc())
				{
					echo "<li>".$arr_subcat['subname']."</li>";
				}
		echo "</ul>";
	}

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)) {
            return false;
        }
		
        return true;

    }

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

    function error()
    {

        return (mysql_error());
    }

    function query($sql = '')

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

    function affectedRows()
    {

        return (@mysql_affected_rows($this->conn));
    }

    function numRows()

    {
        return (@mysql_num_rows($this->result));
    }

	function fieldName($field)
    {
       return (@mysql_field_name($this->result,$field));
    }

	 function insertID()
    {
        return (@mysql_insert_id($this->conn));
    }



    function fetchObject()
    {
        return (@mysql_fetch_object($this->result, MYSQL_ASSOC));
    }



    function fetchArray()
    {
        return (@mysql_fetch_array($this->result, MYSQL_NUM));
    }



    function fetchAssoc()
    {
        return (@mysql_fetch_assoc($this->result));
    }



    function freeResult()
    {
        return (@mysql_free_result($this->result));
    }

}