SQL Domain

The SQL Domain is a construct introduced in Oracle Database 23ai that lets you define a reusable domain for a column: a base type (e.g. VARCHAR2(20)), a CHECK constraint, a DEFAULT value, and optional annotations metadata — all encapsulated in a data dictionary object that can be reused on many different columns.

How it works #

You declare it with CREATE DOMAIN name AS base_type ... CONSTRAINT chk_X CHECK (...) DEFAULT ... ANNOTATIONS (...). Once created, the domain is visible in DBA_DOMAINS and can be used as a column type in any CREATE TABLE. Oracle validates the domain’s CHECK on every INSERT/UPDATE just as it would for an inline constraint.

What it’s for #

Centralizing in one place the domain of a column, avoiding replication of the same value list (or same constraint) across dozens of tables. When the set evolves, a single ALTER DOMAIN propagates the change to all columns using the domain — no need to touch the CREATE TABLEs or run multiple ALTER TABLEs.

What sets it apart from PostgreSQL DOMAIN #

PostgreSQL’s DOMAIN has existed for much longer but is more minimal: base type + constraints, no annotations system. Oracle added a metadata layer (display, description, ordering, etc.) that BI tools, reporting systems and UI generation frameworks can read to automatically derive labels, visual ordering, field descriptions.