ClickHouse/docs/en/sql-reference/dictionaries/index.md

toc_folder_title	toc_priority	toc_title
Dictionaries	35	Introduction

Dictionaries

A dictionary is a mapping (key -> attributes) that is convenient for various types of reference lists.

ClickHouse supports special functions for working with dictionaries that can be used in queries. It is easier and more efficient to use dictionaries with functions than a JOIN with reference tables.

ClickHouse supports:

• Built-in dictionaries with a specific set of functions.
• Plug-in (external) dictionaries with a set of functions.