PHP - MYSQL - 测试数据库服务器(PHP - MYSQL - test datab

我正在学习PHP MYSQL，并试图建立一个数据库。

我下面这个教程http://www.raywenderlich.com/2941/how-to-write-a-simple-phpmysql-web-service-for-an-ios-app

到目前为止，我测试，看看如果服务器有到MySQL访问。当我使用下面的代码。

?php

class RedeemAPI {
   private $db;

   // Constructor - open DB connection
   function __construct() {
       $this->db = new mysqli('localhost', 'username', 'password', 'promos');
    $this->db->autocommit(FALSE);
}

// Destructor - close DB connection
function __destruct() {
    $this->db->close();
}

// Main method to redeem a code
function redeem() {
    // Print all codes in database
    $stmt = $this->db->prepare('SELECT id, code, unlock_code, uses_remaining FROM rw_promo_code');
    $stmt->execute();
    $stmt->bind_result($id, $code, $unlock_code, $uses_remaining);
    while ($stmt->fetch()) {
        echo "$code has $uses_remaining uses remaining!";
    }
    $stmt->close();
   }
} 
// This is the first thing that gets called when this page is loaded
// Creates a new instance of the RedeemAPI class and calls the redeem method
$api = new RedeemAPI;
$api->redeem();

?

我得到以下错误：

Warning: mysqli::mysqli() [mysqli.mysqli]: [2002] No such file or directory (trying to connect via unix:///var/mysql/mysql.sock) in /Users/user/Sites/promos/index.php on line 8

Warning: mysqli::mysqli() [mysqli.mysqli]: (HY000/2002): No such file or directory in /Users/user/Sites/promos/index.php on line 8

Warning: mysqli::autocommit() [mysqli.autocommit]: Couldn't fetch mysqli in /Users/user/Sites/promos/index.php on line 9

Warning: mysqli::prepare() [mysqli.prepare]: Couldn't fetch mysqli in /Users/user/Sites/promos/index.php on line 20

Fatal error: Call to a member function execute() on a non-object in /Users/user/Sites/promos/index.php on line 21

难道我也许忘记启用的东西吗？

这或许可以解释为什么我无法通过我的IP地址，续集专业，只为127.0.0.1连接？