Controlling user-defined functions
User-defined functions are extensions to the SQL language, which you can invoke in an SQL statement wherever you can use expressions or built-in functions.
About this task
Introductory concepts
User-defined functions, like stored procedures,
run in WLM-established address spaces. 
Because
new functions are sometimes added to DB2®,
it is best to fully qualify references to user-defined functions,
or set the value of the CURRENT PATH special register, so that the
references resolve to the correct function in the event of a name
conflict.
Procedure
Issue the appropriate command for the action that you want
to take. 
- START FUNCTION SPECIFIC
- Activates an external function that is stopped.
- DISPLAY FUNCTION SPECIFIC
- Displays statistics about external user-defined functions accessed by DB2 applications.
- STOP FUNCTION SPECIFIC
- Prevents DB2 from accepting SQL statements with invocations of the specified functions.