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Domain

A domain (sometimes referred to as a "derived type") is a user-defined data type based on an existing data type, typically to provide what is effectively a common definiion of a check constraint, which can be used in multiple table definitions.

Caveats

Unlike a regular constraint, while any constraints applied to the domain will be checked when converting a column to the domain type, or inserting the column, they will not be checked retroactively if the domain definition is modified.

Change history

• PostgreSQL 9.1
  • collation support added (commit 414c5a2e)
• PostgreSQL 7.4
  • ALTER DOMAIN command added (commit 17194f41)
  • support for CHECK expressions added (commit 6b603e67)
• PostgreSQL 7.3
  • added (commit 01c76f74)

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References

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