protected function getOrder(array $queryParts)
    {
        if (isset($queryParts['order'])) {
            $order = [];

            foreach ($queryParts['order'] as $array) {
                $order[] =
                    $this->quoteIdentifier($array[0]) .
                    (strtolower($array[1]) === 'asc' ? ' ASC' : ' DESC');
            }

            return 'ORDER BY ' . implode(', ', $order);
        }

        return null;
    }