Re: set-level update fails with unique constraint violation

# scott(dot)marlowe(at)gmail(dot)com / 2010-01-02 11:23:24 -0700:
> On Sat, Jan 2, 2010 at 1:40 AM, Roman Neuhauser <neuhauser(at)sigpipe(dot)cz> wrote:
> > # david(at)fetter(dot)org / 2009-12-31 08:04:58 -0800:
> >> On Thu, Dec 31, 2009 at 10:52:20AM +0100, neuhauser+pgsql-general#postgresql(dot)org(at)sigpipe(dot)cz wrote:
> >> > Hello,
> >> >
> >> > this fails with "duplicate key value":
> >> >
> >> >     CREATE TABLE x (
> >> >       i INT NOT NULL UNIQUE
> >> >     );
> >> >     INSERT INTO x (i) VALUES (1), (2), (3);
> >> >     UPDATE x SET i = i + 1;
> >> >
> >> > are there any plans to make this work?
> >>
> >> This will work in 8.5:
> >>
> >> CREATE TABLE x (
> >>     i int NOT NULL UNIQUE DEFERRABLE INITIALLY DEFERRED
> >> );
> >> INSERT INTO x (i) VALUES (1), (2), (3);
> >> UPDATE x SET i = i + 1;
> >
> > thanks, this might be a bearable workaround in some cases
> > provided there's also SET CONSTRAINTS ... DEFERRED / IMMEDIATE.
> > what I really want is a mode that fires the constraint check
> > at the end of the statement.
>
> What advantage would there be to a constraint that fires right after
> to one that fires at the end of the transaction?

What? I didn't say that. I'm saying that I want IMMEDIATE constraint
that is atomic with regard to the statement. It's obvious that

UPDATE x SET i = i + 1

cannot break a UNIQUE constraint on x.i lest the constraint checking
is not atomic.

I can see how such non-atomic checking can be good performance-wise,
but I'm more interested in logical correctness.

--
Roman Neuhauser