> engine. Part of my job, however, is to be (sometimes painfully!)
> aware of the subtle differences between 9+ different SQL engines.

That is main problem - the more engines you know,
the less you know each of them.
Regarding UDFs and null handling - I think you would save lot of time
if you just write your own (after all they are *user* defined functions)
instead of endlessly testing/comparing someone else's work.

Ivan