your code snippet is only a little part of the complete solution:
- you would need some code to provide the parameter and get the result
- you would need some command to create your RPG
- you would need some SQL script to wrap this as UDF
- finally you would need some method to let your SQL script run
=> two diffrent sources minimum and two steps to come to the result and you
must have knowledge in two diffrent languages.
My true opinion: this would be easier and more readable to do it completely