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23 lines
879 B
Markdown
23 lines
879 B
Markdown
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---
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# 字典 {#dictionaries}
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字典是一个映射 (`key -> attributes`）这是方便各种类型的参考清单。
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ClickHouse支持使用可用于查询的字典的特殊功能。 这是更容易和更有效地使用字典与功能比 `JOIN` 与参考表。
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[NULL](../syntax.md#null) 值不能存储在字典中。
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ClickHouse支持:
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- [内置字典](internal_dicts.md#internal_dicts) 具有特定的 [功能集](../../sql_reference/functions/ym_dict_functions.md).
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- [插件（外部）字典](external_dictionaries/external_dicts.md) 用一个 [职能净额](../../sql_reference/functions/ext_dict_functions.md).
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[原始文章](https://clickhouse.tech/docs/en/query_language/dicts/) <!--hide-->
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