protected function getSet(array $queryParts)
    {
        if (isset($queryParts['set']) && !empty($queryParts['set'])) {
            $updates = array();

            foreach ($queryParts['set'] as $k => $v) {
                $updates[] = sprintf(
                    '%s = %s',
                    $this->quoteIdentifier($k),
                    $this->quote($v)
                );
            }

            return 'SET ' . implode(', ', $updates);
        }

        return null;
    }