Re: How to notice column changes in trigger

Josh Berkus wrote:
>
> Andreas,
>
> > 1) update test set a=0 -> trigger does its work
> > 2) update test set a=0, b=1, c=2 -> trigger does nothing
> > 3) update test set a=0, b=b, c=c -> trigger does nothing, but content of
> > a and b dont change either although touched
>
> > IF OLD.b=NEW.b will not work, case 3) will falsely execute the trigger
> > code.
>
> I still don't get why you'd want to do this. Can you provide are real-world
> example where there is a difference between setting B=B and not updating B?

Setting b=b and not updating it is indeed identical ... at least after
the targetlist completion in PostgreSQL. But it is different from
b=<b's-old-value>, and the fact that we cannot distinguish between these
two (inside the trigger) prevents us from skipping foreign key checks if
your fk-values haven't been touched.

Jan

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