CREATE DOMAIN

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Syntax

create_domain ::= CREATE DOMAIN domain_name AS data_type
                  [ DEFAULT expression ]
                  [ NOT NULL ]
                  [ constraint_definition [, ...] ]

domain_name ::= [schema.]name

constraint_definition ::= CHECK ( expression )
                        | CONSTRAINT constraint_name CHECK ( expression )

• Schema-qualified names: Domains can be defined in specific schemas
• Base types: Any valid PostgreSQL data type as the underlying type
• Default values: Default expressions for the domain
• NOT NULL constraints: Enforce non-null values
• CHECK constraints:
  • Anonymous CHECK constraints
  • Named constraints with CONSTRAINT clause
  • Multiple constraints per domain
  • Expressions using VALUE keyword to reference the domain value

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Canonical Format

-- Simple domain without constraints
CREATE DOMAIN [schema.]domain_name AS data_type;

-- Domain with constraints (multi-line format)
CREATE DOMAIN [schema.]domain_name AS data_type
  [ DEFAULT expression ]
  [ NOT NULL ]
  [ CONSTRAINT constraint_name CHECK ( expression ) ]
  [ CHECK ( expression ) ];

• Uses single-line format for simple domains without constraints
• Uses multi-line format with indentation when domain has constraints, defaults, or NOT NULL
• DEFAULT clause appears before NOT NULL when both are present
• Named constraints use CONSTRAINT constraint_name prefix
• Anonymous constraints are listed without the CONSTRAINT keyword
• Each constraint is on its own indented line for readability
• For DROP operations: DROP DOMAIN IF EXISTS domain_name RESTRICT;