ClickHouse/docs/zh/sql-reference/dictionaries/external-dictionaries/external-dicts.md
Ivan Blinkov cd14f9ebcb
SQL reference refactoring (#10857)
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# 外部字典 {#dicts-external-dicts}
您可以从各种数据源添加自己的字典。 字典的数据源可以是本地文本或可执行文件、HTTP(s)资源或其他DBMS。 有关详细信息,请参阅 “[外部字典的来源](external-dicts-dict-sources.md)”.
ClickHouse:
- 完全或部分存储在RAM中的字典。
- 定期更新字典并动态加载缺失的值。 换句话说,字典可以动态加载。
- 允许创建外部字典与xml文件或 [DDL查询](../../statements/create.md#create-dictionary-query).
外部字典的配置可以位于一个或多个xml文件中。 配置的路径在指定 [dictionaries\_config](../../../operations/server-configuration-parameters/settings.md#server_configuration_parameters-dictionaries_config) 参数。
字典可以在服务器启动或首次使用时加载,具体取决于 [dictionaries\_lazy\_load](../../../operations/server-configuration-parameters/settings.md#server_configuration_parameters-dictionaries_lazy_load) 设置。
该 [字典](../../../operations/system-tables.md#system_tables-dictionaries) 系统表包含有关在服务器上配置的字典的信息。 对于每个字典,你可以在那里找到:
- 字典的状态。
- 配置参数。
- 度量指标如为字典分配的RAM量或自成功加载字典以来的查询数量。
字典配置文件具有以下格式:
``` xml
<yandex>
<comment>An optional element with any content. Ignored by the ClickHouse server.</comment>
<!--Optional element. File name with substitutions-->
<include_from>/etc/metrika.xml</include_from>
<dictionary>
<!-- Dictionary configuration. -->
<!-- There can be any number of <dictionary> sections in the configuration file. -->
</dictionary>
</yandex>
```
你可以 [配置](external-dicts-dict.md) 同一文件中的任意数量的字典。
[字典的DDL查询](../../statements/create.md#create-dictionary-query) 在服务器配置中不需要任何其他记录。 它们允许使用字典作为一流的实体,如表或视图。
!!! attention "注意"
您可以通过在一个小字典中描述它来转换小字典的值 `SELECT` 查询(见 [变换](../../../sql-reference/functions/other-functions.md) 功能)。 此功能与外部字典无关。
## 另请参阅 {#ext-dicts-see-also}
- [配置外部字典](external-dicts-dict.md)
- [在内存中存储字典](external-dicts-dict-layout.md)
- [字典更新](external-dicts-dict-lifetime.md)
- [外部字典的来源](external-dicts-dict-sources.md)
- [字典键和字段](external-dicts-dict-structure.md)
- [使用外部字典的函数](../../../sql-reference/functions/ext-dict-functions.md)
[原始文章](https://clickhouse.tech/docs/en/query_language/dicts/external_dicts/) <!--hide-->