每当我在pdo连接之后传递查询时，页面都返回一个500错误。我不知道是什么引起了这个问题。我用的是lamp服务器。代码如下：

$user = 'root';
$database = 'mysql';
$password = 'root';
$dbname = 'pdotest';
$host = 'localhost';

$dsn = $database . ":" . $host . ";dbname=" . $dbname;

$opt = array(
    PDO::ATTR_ERRMODE => PDO::ERRMODE_EXCEPTION,
    PDO::ATTR_DEFAULT_FETCH_MODE => PDO::FETCH_OBJ,
);

$pdo = new PDO($dsn, $user, $password, $opt) or die('Can\'t establish connection');

// This is where it gives 500 error

$stmt = $pdo->query("SELECT * FROM pdo");