Descriptors allow NULL signalling no matter the type of data. The fbudf library makes ample use of this technique. Unfortunately, using descriptors is rather cumbersome; it’s more work and less play for the UDF with the click of a button. They do this by poking a value directly into a system table. This technique is neither recommended nor supported by Firebird, and although until now it works in practice,

batch mode, this can be acceptable — as usual, it depends on your needs. If you want to use this technique and allow users to trigger the SP at any time, you must make sure by other means that the SP can

drive, a filesystem share or a network filesystem. (Well, you can, but you shouldn’t, and this technique isn’t covered here.)  You can open a read-only database from a read-only medium like a DVD, but

=============== 128 SQL> commit; To get back to the command prompt type quit or exit.  The above technique, as demonstrated, works, but ideally databases and metadata objects should be created and maintained