Dictionary

A dictionary is a mapping (key -> attributes) that can be used as a function for queries, offering a simpler and more efficient approach compared to the JOIN method of reference tables.

There are two types of data dictionaries: built-in dictionaries and external dictionaries.

Built-in Dictionary

ClickHouse supports a built-in dictionary  called geobase. The supported functions can be referenced in Functions for working with Yandex.Metrica dictionaries .

External Dictionary

ClickHouse can add external dictionaries  from multiple data sources. Supported data sources can be found at Sources Of External Dictionaries .