PostgreSQL user-defined data types

PostgreSQL provides two methods for implementing user-defined data types through the following commands:

• CREATE DOMAIN: The CREATE DOMAIN command allows developers to create a user-defined data type with constraints. This helps in making the source code more modular.

• CREATE TYPE: The CREATE TYPE command is often used to create a composite type, which is useful in procedural languages, and is used as the return data type. Also, one can use the create type to create the ENUM type, which is useful in decreasing the number of joins, specifically for lookup tables.

Often, developers tend not to use the user-defined data types, and use flat tables instead due to a lack of support on the driver side, such as JDBC and ODBC. Nonetheless, in JDBC, the composite data types can be retried as Java objects and parsed manually.

The PostgreSQL CREATE DOMAIN command

Domain is a data type with optional constraints, and as with other database objects it should have a unique...