mirror of
https://github.com/ClickHouse/ClickHouse.git
synced 2024-12-18 12:22:12 +00:00
21 lines
908 B
Markdown
21 lines
908 B
Markdown
---
|
||
toc_folder_title: Dictionaries
|
||
toc_priority: 35
|
||
toc_title: Introduction
|
||
---
|
||
|
||
# Dictionaries {#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.
|
||
|
||
[NULL](../syntax.md#null) values can’t be stored in a dictionary.
|
||
|
||
ClickHouse supports:
|
||
|
||
- [Built-in dictionaries](internal_dicts.md#internal_dicts) with a specific [set of functions](../../sql_reference/functions/ym_dict_functions.md).
|
||
- [Plug-in (external) dictionaries](external_dictionaries/external_dicts.md) with a [net of functions](../../sql_reference/functions/ext_dict_functions.md).
|
||
|
||
[Original article](https://clickhouse.tech/docs/en/query_language/dicts/) <!--hide-->
|