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46 lines
2.2 KiB
Markdown
46 lines
2.2 KiB
Markdown
# External Dictionaries {#dicts-external_dicts}
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You can add your own dictionaries from various data sources. The data source for a dictionary can be a local text or executable file, an HTTP(s) resource, or another DBMS. For more information, see "[Sources for external dictionaries](external_dicts_dict_sources.md)".
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ClickHouse:
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- Fully or partially stores dictionaries in RAM.
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- Periodically updates dictionaries and dynamically loads missing values. In other words, dictionaries can be loaded dynamically.
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- Allows to create external dictionaries with xml-files or [DDL queries](../create.md#create-dictionary-query).
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The configuration of external dictionaries can be located in one or more xml-files. The path to the configuration is specified in the [dictionaries_config](../../operations/server_settings/settings.md#server_settings-dictionaries_config) parameter.
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Dictionaries can be loaded at server startup or at first use, depending on the [dictionaries_lazy_load](../../operations/server_settings/settings.md#server_settings-dictionaries_lazy_load) setting.
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The dictionary configuration file has the following format:
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```xml
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<yandex>
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<comment>An optional element with any content. Ignored by the ClickHouse server.</comment>
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<!--Optional element. File name with substitutions-->
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<include_from>/etc/metrika.xml</include_from>
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<dictionary>
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<!-- Dictionary configuration. -->
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<!-- There can be any number of <dictionary> sections in the configuration file. -->
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</dictionary>
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</yandex>
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```
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You can [configure](external_dicts_dict.md) any number of dictionaries in the same file.
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[DDL queries for dictionaries](../create.md#create-dictionary-query) doesn't require any additional records in server configuration. They allow to work with dictionaries as first-class entities, like tables or views.
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!!! attention
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You can convert values for a small dictionary by describing it in a `SELECT` query (see the [transform](../functions/other_functions.md) function). This functionality is not related to external dictionaries.
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**See also**
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- [Functions for Working with External Dictionaries](../functions/ext_dict_functions.md)
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[Original article](https://clickhouse.yandex/docs/en/query_language/dicts/external_dicts/) <!--hide-->
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