Author: Yegor Andreenko

This is a cross-post from: (https://medium.com/@f1yegor/clickhouse-primary-keys-2cf2a45d7324)

Special thanks to Alexey Milovidov, ClickHouse developer, for providing material for this article.

Recently I dived deep into ClickHouse. ClickHouse is column-store database by Yandex with great performance for analytical queries. For example check benchmark and post of Mark Litwintschik.

Jul 10, 2017   
The guest article from ClickHouse evangelist Yegor Andreenko (@f1yegor) about an interesting extension of aggregate functions aggregate states, that can be used to pre-aggregate data that usually has to be kept in raw, like uniques.