Pagekit\Database\Table::addUniqueIndex PHP Method

    public function addUniqueIndex(array $columnNames, $indexName = null, array $options = array())
    {
        if ($indexName) {
            $indexName = $this->connection->replacePrefix($indexName);
        }
        $this->table->addUniqueIndex($columnNames, $indexName, $options);
        return $this;
    }