SQL插入查询不工作（更新）

Question

这是我昨天问过的问题的扩展，但我无法找到解决问题的方法。这是我当前的代码，它似乎打破了$ result：

$host = 'localhost';
$user = 'dbuser';
$dbpass = 'password';
$dbname = 'users';
$cxn = mysqli_connect($host,$user,$dbpass,$dbname) or die("Could not connect to server.");

$email = $_POST['email'];
        $username = $_POST['username'];
        $first_name = $_POST['first_name'];
        $last_name = $_POST['last_name'];
        $safe_email = mysqli_real_escape_string($cxn,$email);
        $safe_username = mysqli_real_escape_string($cxn,$username);
        $safe_first = mysqli_real_escape_string($cxn,$first_name);
        $safe_last = mysqli_real_escape_string($cxn,$last_name);

        $query = "insert into `user_data` (`email`, `username`, `first_name`, `last_name`) values ('$safe_email', '$safe_username', '$safe_first', '$safe_last')";
        $result = mysqli_query($cxn,$query) or die('Can\'t complete query.');
        echo "Congratulations!"; 

我已经检查了我网站上的错误报告，并且没有显示提交表单时创建的任何错误。我给了'dbuser＆＃39;表的以下特权：INSERT，SELECT，UPDATE，DELETE和CREATE TEMPORARY TABLES。我还没有改变数据库本身的任何主要设置。