Should we document how column DEFAULT expressions work? - Mailing list pgsql-hackers

From David G. Johnston
Subject Should we document how column DEFAULT expressions work?
Date
Msg-id CAKFQuwZ89s_3ytHw58_o=BFxhpdTwR4UbyDXmOSa05fUFfmFew@mail.gmail.com
Whole thread Raw
In response to Re: Should we document how column DEFAULT expressions work?  (David Rowley <dgrowleyml@gmail.com>)
Responses Re: Should we document how column DEFAULT expressions work?
List pgsql-hackers
On Wednesday, October 16, 2024, Bruce Momjian <bruce@momjian.us> wrote:
On Fri, Jul  5, 2024 at 05:11:22PM -0400, Bruce Momjian wrote:
> On Fri, Jul  5, 2024 at 05:03:35PM -0400, Tom Lane wrote:
> > Bruce Momjian <bruce@momjian.us> writes:
> > > Well, 'now()' certainly _looks_ like a function call, though it isn't.
> > > The fact that 'now()'::timestamptz and 'now'::timestamptz generate
> > > volatile results via a function call was my point.
> >
> > The only reason 'now()'::timestamptz works is that timestamptz_in
> > ignores irrelevant punctuation (or what it thinks is irrelevant,
> > anyway).  I do not think we should include examples that look like
> > that, because it will further confuse readers who don't already
> > have a solid grasp of how this works.
>
> Wow, I see that now:
>
>       test=> SELECT 'now('::timestamptz;
>                 timestamptz
>       -------------------------------
>        2024-07-05 17:04:33.457915-04
>
> If I remove the 'now()' mention in the docs, patch attached, I am
> concerned people will be confused whether it is the removal of the
> single quotes or the use of "()" which causes insert-time evaluation,
> and they might try 'now()'.

Does anyone like this patch?  I changed now()::timestamptz to
now::timestamptz.

I do not, but maybe I’m being overly pedantic.  All string literals are parsed during the create table command.  It’s only the situations where that parsing is non-deterministic that cause an issue.

Is there anything wrong with the patch I proposed?

David J.

pgsql-hackers by date:

Previous
From: Matthias van de Meent
Date:
Subject: Re: Limiting overshoot in nbtree's parallel SAOP index scans
Next
From: Bruce Momjian
Date:
Subject: Re: minor doc issue in 9.16.2.1.1. Boolean Predicate Check Expressions