PHP萬能串連資料庫方法

<?php class DB {    const HOST='127.0.0.1';    const USER='root';    const PASS='root';    const DATA='mooc';    static public $_instance;    private function __construct() {    mysql_connect(DB::HOST,DB::USER,DB::PASS);    mysql_set_charset('utf8');    mysql_select_db(DB::DATA);}public static function getInstance() {    if(!self::$_instance instanceof self) {    self::$_instance=new self;}return self::$_instance;}} $model=DB::getInstance();    //串連資料庫，並且測試 $sql="select * from user";    $res=mysql_query($sql);    while($row=mysql_fetch_assoc($res)) {    var_dump($row);}?>