Ideally, I'd like to generate invoice numbers as an auto-incremented field where the seed value is stored in a table.

On insert the value should be seed value + 1 and the seed value should be updated accordingly.

I've tried a few things (and failed miserably) and would appreciate any ideas on the subject.

Just in case you're wondering: I can't start from scratch with an auto-incremented field because of inherited data.

TIA