User-defined functions

User-defined functions are small programs that you can write to perform an operation. You can use a user-defined function wherever you can use a built-in function.

The CREATE FUNCTION statement is used to explicitly create a user-defined function.

Example

Assume that you define a distinct type called US_DOLLAR. You might want to allow instances of US_DOLLAR to be added. You can create a user-defined function that uses a built-in addition operation and takes instances of US_DOLLAR as input. This function, called a sourced function, requires no application coding. Alternatively, you might create a more complex user-defined function that can take a US_DOLLAR instance as input and then convert from U.S. dollars to another currency.

You name the function and specify its semantics so that the function satisfies your specific programming needs.