2020-04-08 14:22:25 +00:00
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2020-05-15 04:34:54 +00:00
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2020-04-08 14:22:25 +00:00
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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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2020-05-06 06:13:29 +00:00
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[NULL](../../sql-reference/syntax.md#null-literal) 值不能存储在字典中。
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2020-04-08 14:22:25 +00:00
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ClickHouse支持:
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2020-04-30 18:19:18 +00:00
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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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2020-05-15 04:34:54 +00:00
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- [插件（外部）字典](external-dictionaries/external-dicts.md#dicts-external-dicts) 用一个 [功能集](../../sql-reference/functions/ext-dict-functions.md).
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2020-04-08 14:22:25 +00:00
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[原始文章](https://clickhouse.tech/docs/en/query_language/dicts/) <!--hide-->
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