The following CREATE FUNCTION request has input parameters of the ST_GEOMETRY type, specifies the method st_within in its RETURN statement, and returns an INTEGER value from the invocation of st_within.
CREATE FUNCTION test.geospatial_type_udf (a ST_GEOMETRY, b ST_GEOMETRY) RETURNS INTEGER LANGUAGE SQL DETERMINISTIC CONTAINS SQL SPECIFIC test.geospatial_type_UDF CALLED ON NULL INPUT SQL SECURITY DEFINER COLLATION INVOKER INLINE TYPE 1 RETURN a.st_within(b);