ASA SQL User's Guide
  Using Procedures, Triggers, and Batches
    The structure of procedures and triggers

Passing parameters to functions

User-defined functions are not invoked with the CALL statement, but are used in the same manner that built-in functions are. For example, the following statement uses the fullname function defined in Creating user-defined functions to retrieve the names of employees:

To list the names of all employees

• Type the following:

  SELECT fullname(emp_fname, emp_lname) AS Name
  FROM employee

Notes 

• Default parameters can be used in calling functions. However, parameters cannot be passed to functions by name.

• Parameters are passed by value, not by reference. Even if the function changes the value of the parameter, this change is not returned to the calling environment.

• Output parameters cannot be used in user-defined functions.

• User-defined functions cannot return result sets.