是什么导致include_once用MySQL破坏PHP中的代码？
What would cause include_once to break my code in PHP with MySQL?

以下代码无法正常工作：

    public function __construct($thread_id)
    {
        require_once('../private/mysqli_connect.php');
        require_once('../php_classes/class_message.php');

        $this->thread_id=$thread_id;

        $q="SELECT *
        FROM message_thread_name
        WHERE thread_id=2";

        if($r=@mysqli_query($dbc, $q))
        {
            while($row=mysqli_fetch_array($r, MYSQLI_ASSOC))
            {
                $this->poster=$row['name'];
                $this->subject=$row['thread_subject'];
            }
        }

        $qm="SELECT message_id
        FROM message
        WHERE thread_id=$this->thread_id";

        if($rm=@mysqli_query($dbc, $rm))
        {
            while($rowm=mysqli_fetch_array($rm, MYSQLI_ASSOC))
            {
                $message=new message($rowm['message_id']);
                array_push($this->messages, $message);
            }
        }
    }

我没有解决它的想法，所以我更改了require_once('../private/mysqli_connect.php'); require('../private/mysqli_connect.php'); ，令我惊讶的是，它确实奏效了。 关于为什么会这样的任何想法？

谢谢。