Thanks to all of you who took the time to comment on my question.

I've learnt something too from your suggestions: I'll be using the nullif tip and looking into persisted columns.

The Arithabort part was added because I imagined Hugo critiquing my question, - and as I have been caught out by other questions which didn't explicitally state such detail, I wanted to make sure there could be no room for ambiguity.

Incidentally if anyone is toying with the idea of submitting a question for QOTD - imagine Hugo reading it before you submit, it will sharpen your thinking. 😉