Specify overloaded routines during invocation

When you invoke an overloaded routine, you must specify an argument list for the routine. If you invoke an overloaded routine by the routine name only, the routine-resolution process fails because the database server cannot uniquely identify the routine without the arguments.

For example, the following SQL statement shows how you can invoke the overloaded equal() function on a new data type, udtype1: 
CREATE TABLE atest (col1 udtype1, col2 udtype1, ...)
...
SELECT * FROM employee WHERE equal(col1, col2)
Because the equal() function is an operator function bound to the equal (=) symbol, you can also invoke the equal() function with an argument on either side of the operator symbol, as follows:
SELECT * FROM employee WHERE col1 = col2
In SPL, the following statements show ways that you can invoke the equal() function:
EXECUTE FUNCTION equal(col1, col2) INTO result

CALL equal(col1, col2) RETURNING result
LET result = equal(col1, col2)

For more information about overloaded operator functions, refer to Extend operators and built-in functions.