Re: autoupdating mtime column

"David Garamond" <davidgaramond@gmail.com> writes:
> On 8/4/06, Richard Huxton <dev@archonet.com> wrote:
>> Just check for OLD.mtime = NEW.mtime, or am I missing something here?

> How do I differentiate between:
> UPDATE t SET mtime=mtime ...;
> in which mtime is specifically set and should not change,

You don't.  A trigger has no way to know the history of the row it's
looking at --- consider the possibility that it was already modified
by earlier triggers.

If you are really intent on having a way to suppress the mtime update
you could dedicate an additional field to the purpose, eg

UPDATE t SET foo=..., bar=..., keepmtime = true ...

and in the trigger something like
if new.keepmtime then    new.keepmtime = false;else    new.mtime = now();

As long as nothing else ever touches keepmtime this would work.
Personally I'm dubious that it's worth the trouble --- do you
have a real use-case for suppressing mtime updates?
        regards, tom lane