Writing external user-defined functions

Just as with stored procedures, we can also define user-defined functions written in high-level programming languages. These are known as external UDFs. They can also be used in the same way as SQL functions. Complex business logic can be better implemented in high-level programming languages, hence giving better flexibility. By using external functions, we can maintain state between iterative invocations of the function. External functions can access external objects as well, such as a server filesystem, system calls, and so on. One limitation for external functions is that we cannot return result sets. In this recipe, we will see how we can design external user-defined functions.

External functions are supported in the following languages:

• C/C++

• Java

• OLE

• .NET common language runtime languages

How to do it...

Just like stored procedures, we need to define the function body in a programming language and register the function in DB2. We will use Java as an...