public function formatTableUnique(array $data) {
        $key = sprintf($this->getClause(self::UNIQUE_KEY), $this->quote($data['index']), $this->quoteList($data['columns']));

        if ($data['constraint']) {
            $key = sprintf($this->getClause(self::CONSTRAINT), $this->quote($data['constraint'])) . ' ' . $key;
        }

        return $key;
    }