Modifiers in a C UDR

The following table shows the routine modifiers that are valid for C routines.


Routine modifier	Description	Valid for external function	Valid for external procedure
CLASS	Specifies a virtual-processor class in which to run the UDR	Yes	Yes
COSTFUNC	Specifies the name of the cost function for this UDR	Yes	Yes
HANDLESNULLS	Specifies that the UDR can handle null arguments	Yes	Yes
INTERNAL	Specifies that the UDR is an internal routine; that is, that the routine is not available for use in an SQL or SPL statement	Yes	Yes
ITERATOR	Specifies that the UDR is an iterator function	Yes	No
NEGATOR	Specifies that the UDR is a negator function	Yes	No
NOT VARIANT	Specifies that all invocations of the UDR with the same arguments return the same value	Yes	No
PARALLELIZABLE	Routine can be executed in parallel	Yes	Yes
PERCALL_COST	Specifies the cost of execution for the UDR	Yes	Yes
SELCONST	Specifies the selectivity of the UDR	Yes	No
SELFUNC	Specifies the name of the selectivity function for this UDR	Yes	No
STACK	Specifies the stack size for the UDR	Yes	Yes
VARIANT	Specifies that all invocations of the UDR with the same arguments do not necessarily return the same value	Yes	No

The following example shows how to use the WITH clause to specify a set of modifiers when you create an external-language function:

CREATE FUNCTION lessthan (arg1 basetype2, arg2 basetype2)
RETURNING BOOLEAN
WITH (HANDLESNULLS, NOT VARIANT)
EXTERNAL NAME '/usr/lib/basetype2/lib/libbtype2.so(basetype2_lessthan)'
LANGUAGE C

In this example, the HANDLESNULLS modifier indicates that the basetype2_lessthan() function (in the shared library /usr/lib/basetype2/lib/libbtype2.so) is coded to recognize SQL null. If HANDLESNULL is not set, the routine manager does not execute the UDR if any arguments of the routine are null; it simply returns null.