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26 lines
1.2 KiB
Markdown
26 lines
1.2 KiB
Markdown
# Domains
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Domains are special-purpose types, that add some extra features atop of existing base type, leaving on-wire and on-disc format of underlying table intact. At the moment, ClickHouse does not support user-defined domains.
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You can use domains anywhere corresponding base type can be used:
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* Create a column of domain type
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* Read/write values from/to domain column
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* Use it as index if base type can be used as index
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* Call functions with values of domain column
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* etc.
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### Extra Features of Domains
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* Explicit column type name in `SHOW CREATE TABLE` or `DESCRIBE TABLE`
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* Input from human-friendly format with `INSERT INTO domain_table(domain_column) VALUES(...)`
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* Output to human-friendly format for `SELECT domain_column FROM domain_table`
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* Loading data from external source in human-friendly format: `INSERT INTO domain_table FORMAT CSV ...`
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### Limitations
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* Can't convert index column of base type to domain type via `ALTER TABLE`.
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* Can't implicitly convert string values into domain values when inserting data from another column or table.
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* Domain adds no constrains on stored values.
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[Original article](https://clickhouse.yandex/docs/en/data_types/domains/overview) <!--hide--> |