PostgreSQL, Second Edition

Creating Your Own Data Types

PostgreSQL allows you to create your own data types. This is not unique among relational database systems, but PostgreSQL's depth of support is unique. In other RDBMSs, you can define one data type in terms of another (predefined) data type. For example, you might create a new numeric data type to hold an employee's age, with valid values between 18 and 100. This is still a numeric data type—you must define the new type as a subset of an existing type. PostgreSQL calls such a “refined” data type a domain. Starting with PostgreSQL version 8.0, you can also create composite data types. A composite type is a single data type made up of multiple fields. For example, you might define a composite type named address that ...