查询更新功能不起作用

我使用CS50 2014中的以下函数，当我选择时它可以工作，但当我尝试更新时它不工作。以下是查询和函数：

query(
    "UPDATE users 
         SET pwtxt = ?, pass = ?, dt = ?, reset = ?
         WHERE usr  = ?",
    NULL,
    "compass",
    NULL,
    0,
    1
);
function query(/* $sql [, ... ] */)
{
    // SQL statement
    $sql = func_get_arg(0); 
    // parameters, if any
    $parameters = array_slice(func_get_args(), 1);  
    // try to connect to database
    static $handle;
    if (!isset($handle))
    {
        try
        {
            // connect to database
            $handle = new PDO("mysql:dbname=" . DATABASE . ";host=" . SERVER, USERNAME, PASSWORD);
            // ensure that PDO::prepare returns false when passed invalid SQL
            $handle->setAttribute(PDO::ATTR_EMULATE_PREPARES, false);
        }
        catch (Exception $e)
        {
            // trigger (big, orange) error
            trigger_error($e->getMessage(), E_USER_ERROR);
            exit;
        }
    }
    // prepare SQL statement
    $statement = $handle->prepare($sql);
    if ($statement === false)
    {
        // trigger (big, orange) error
        //  trigger_error($handle->errorInfo()[2], E_USER_ERROR);  need to fix array issue
        exit;
    }   
    // execute SQL statement
    $results = $statement->execute($parameters);

    // return result set's rows, if any
    if ($results !== false)
    {       
        return $statement->fetchAll(PDO::FETCH_ASSOC);
    }
    else
    {       
        return false;
    }
}