PostgreSQL, Second Edition

Extending the PostgreSQL Server with Custom Data Types

The customers table in this sample application contains a column named balance. I've made the assumption that the values in the balance column are expressed in local currency (that is, U.S. dollars in the U.S., British pounds in the U.K.). This assumption serves us well until our corner video store opens a web site and starts accepting orders from foreign customers.

PostgreSQL doesn't have a predefined data type that represents a foreign currency value, so let's create one. You want to store three pieces of information for each foreign currency value: the name of the currency (pounds, dollars, drachma, and so on), the number of units, and the exchange rate at the time the foreign currency ...