2020-04-08 14:22:25 +00:00
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---
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# 字典 {#dictionaries}
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2021-05-23 14:12:43 +00:00
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字典是一个映射 (`键 -> 属性`）, 是方便各种类型的参考清单。
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2020-04-08 14:22:25 +00:00
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2021-05-23 14:12:43 +00:00
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ClickHouse支持一些特殊函数配合字典在查询中使用。 将字典与函数结合使用比将 `JOIN` 操作与引用表结合使用更简单、更有效。
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2020-04-08 14:22:25 +00:00
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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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2021-05-23 14:12:43 +00:00
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- [内置字典](internal-dicts.md#internal_dicts) ,这些字典具有特定的 [函数集](../../sql-reference/functions/ym-dict-functions.md).
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- [插件（外部）字典](external-dictionaries/external-dicts.md#dicts-external-dicts) ,这些字典拥有一个 [函数集](../../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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