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.
Domains are special-purpose types that add some extra features atop of existing base type, but leaving on-wire and on-disc format of the underlying data type intact. At the moment, ClickHouse does not support user-defined domains.
You can use domains anywhere corresponding base type can be used:
You can use domains anywhere corresponding base type can be used, for example:
- Create a column of domain type
- Create a column of a domain type
- Read/write values from/to domain column
- Use it as index if base type can be used as index
- Use it as an index if a base type can be used as an index
- Call functions with values of domain column
- etc.
### Extra Features of Domains {#extra-features-of-domains}
- Explicit column type name in `SHOW CREATE TABLE` or `DESCRIBE TABLE`
- Input from human-friendly format with `INSERT INTO domain_table(domain_column) VALUES(...)`
- Output to human-friendly format for `SELECT domain_column FROM domain_table`
- Loading data from external source in human-friendly format: `INSERT INTO domain_table FORMAT CSV ...`
- Loading data from an external source in the human-friendly format: `INSERT INTO domain_table FORMAT CSV ...`
