At the very least that note about this behavior should be highlighted, probably on the Trigger Behavior page and not buried in a bunch of notes on the Create Trigger page.
Judy Loomis <hoodie.judy@gmail.com> writes: > I'm going to have to really look at all my BEFORE UPDATE triggers and make > sure we're not missing any more. > And I have to stop telling management that a trigger means we always know > when a value changes.
Well, you can rely on that, just not like this. Use an AFTER trigger (else, you can't be sure it fires after all the BEFORE triggers) and instead of triggering it with a column parameter, have it do something like "if old.col is distinct from new.col".
Yeah, it's a bit slower that way, but there's no free lunch, especially if you don't trust your other triggers. (Although, if you have so many triggers that that's a problem, I think you might have some other design issues.)
