Stamping rows...

[Michael Fuhr]

I am trying to find a way to stamp all of the rows affected by an update (or
insert) with a unique value.

[snip]

At first I tried to do this as a trigger function. The problem with this
solution is that if I dont have the function called for each row, I cannot
modify those rows. if I DO have the function called for each row, how do
they get the "change_number" they cannot simply call nextval() as it will be
different for each row (they also couldn't call curval() because then who is
ever calling nextval()?)

Have you tried calling nextval() in a FOR EACH STATEMENT trigger
and currval() in a FOR EACH ROW trigger? This works for me in
simple tests. I don't know if statement triggers are guaranteed
to fire before row triggers, but they do appear to work that way.

[Greg Sabino Mullane]

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I am trying to find a way to stamp all of the rows affected by
an update (or insert) with a unique value. For example, consider

...

At first I tried to do this as a trigger function.

You were on the right path:

ALTER TABLE people ADD mtime TIMESTAMPTZ NOT NULL DEFAULT now();

CREATE OR REPLACE FUNCTION update_mtime() RETURNS TRIGGER LANGUAGE PLPGSQL AS
'BEGIN NEW.mtime = now(); RETURN NEW; END;';

CREATE TRIGGER people_update_mtime BEFORE UPDATE ON people
FOR EACH ROW EXECUTE PROCEDURE update_mtime();

(I use a version of this for my incremental backup scheme)

Now every update (or insert) will cause all the rows changed to have the
same unique value. Unless you mess with your system clock. :) As a nice bonus,
you also get to see *when* each row was modified.

- --
Greg Sabino Mullane ***@turnstep.com
PGP Key: 0x14964AC8 200411222111

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[Michael Fuhr]

Post by Greg Sabino Mullane
CREATE OR REPLACE FUNCTION update_mtime() RETURNS TRIGGER LANGUAGE PLPGSQL AS
'BEGIN NEW.mtime = now(); RETURN NEW; END;';
CREATE TRIGGER people_update_mtime BEFORE UPDATE ON people
FOR EACH ROW EXECUTE PROCEDURE update_mtime();
(I use a version of this for my incremental backup scheme)
Now every update (or insert) will cause all the rows changed to have the
same unique value.

Since now() doesn't advance during a transaction, every other update
or insert in the same transaction will get the same "unique" value
even if they were performed as separate statements; that may or may
not meet the requirements for uniqueness. It also assumes that no
two transactions will ever start at exactly the same time.