mirror of
https://github.com/ClickHouse/ClickHouse.git
synced 2024-12-19 21:03:51 +00:00
8623cb232c
* CLICKHOUSE-4063: less manual html @ index.md * CLICKHOUSE-4063: recommend markdown="1" in README.md * CLICKHOUSE-4003: manually purge custom.css for now * CLICKHOUSE-4064: expand <details> before any print (including to pdf) * CLICKHOUSE-3927: rearrange interfaces/formats.md a bit * CLICKHOUSE-3306: add few http headers * Remove copy-paste introduced in #3392 * Hopefully better chinese fonts #3392 * get rid of tabs @ custom.css * Apply comments and patch from #3384 * Add jdbc.md to ToC and some translation, though it still looks badly incomplete * minor punctuation * Add some backlinks to official website from mirrors that just blindly take markdown sources * Do not make fonts extra light * find . -name '*.md' -type f | xargs -I{} perl -pi -e 's//g' {} * find . -name '*.md' -type f | xargs -I{} perl -pi -e 's/ sql/g' {} * Remove outdated stuff from roadmap.md * Not so light font on front page too * Refactor Chinese formats.md to match recent changes in other languages
16 lines
818 B
Markdown
16 lines
818 B
Markdown
# 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-literal) values can't be stored in a dictionary.
|
|
|
|
ClickHouse supports:
|
|
|
|
- [Built-in dictionaries](internal_dicts.md#internal_dicts) with a specific [set of functions](../functions/ym_dict_functions.md#ym_dict_functions).
|
|
- [Plug-in (external) dictionaries](external_dicts.md#dicts-external_dicts) with a [set of functions](../functions/ext_dict_functions.md#ext_dict_functions).
|
|
|
|
|
|
[Original article](https://clickhouse.yandex/docs/en/query_language/dicts/) <!--hide-->
|