Use UDFs in SQL statements

Scalar and column UDFs can be called within an SQL statement almost everywhere that an expression is valid. Table UDFs can be called in the FROM clause of a SELECT. There are a few restrictions of UDF usage, however.

• Use parameter markers or the NULL value as function arguments
  An important restriction involves both parameter markers and the NULL value.
• Use qualified function reference
  If you use a qualified function reference, you restrict the search for a matching function to that schema.
• Use unqualified function reference
  You can use an unqualified function reference instead of a qualified function reference. In this case, DB2's search for a matching function normally uses the function path to qualify the reference.
• Summary of function references
  For both qualified and unqualified function references, the function selection algorithm looks at all the applicable functions, both built-in and user-defined functions, that have the given name, the same number of defined parameters as argument, and each parameter identical to or promotable from the type of the corresponding argument.