DOMAIN (PostgreSQL)

DOMAIN (PostgreSQL) is a SQL data type in the PostgreSQL Specific category. PostgreSQL: creates a reusable custom type with constraints. Like a type alias with validation. The syntax is CREATE DOMAIN domain_name AS base_type [CONSTRAINT name CHECK (condition)];. It returns domain type. A typical example: CREATE DOMAIN us_phone AS TEXT CHECK (VALUE ~ '^\d{3}-\d{3}-\d{4} ); CREATE TABLE contacts ( name TEXT, phone us_phone ); INSERT INTO contacts VALUES ('Alice', '555-123-4567'); -- OK INSERT INTO contacts VALUES ('Bob', '12345'); -- Fails CHECK constraint A close relative is SERIAL, which postgreSQL auto-increment type. Creates an INTEGER column with a sequence. Equivalent to AUTO_INCREMENT in MySQL. A close relative is RETURNING, which postgreSQL extension that returns values from INSERT/UPDATE/DELETE statements (like OUTPUT in SQL Server). A close relative is ARRAY, which postgreSQL supports array columns and array operations. Can be multi-dimensional. More about this category: PostgreSQL-specific features — SERIAL, RETURNING, ARRAY, JSONB, UPSERT.