From: Tom Lane <tgl@sss.pgh.pa.us>
To: David Rowley <dgrowleyml@gmail.com>
cc: "David G. Johnston" <david.g.johnston@gmail.com>,
        James Coleman <jtc331@gmail.com>,
        pgsql-hackers <pgsql-hackers@postgresql.org>
Subject: Re: Should we document how column DEFAULT expressions work?
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Comments: In-reply-to David Rowley <dgrowleyml@gmail.com>
	message dated "Wed, 26 Jun 2024 16:50:00 +1200"
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Date: Wed, 26 Jun 2024 01:12:57 -0400
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David Rowley <dgrowleyml@gmail.com> writes:
> If people don't properly understand these special timestamp input
> values, then maybe the documentation in [1] needs to be improved.  At
> the moment the details are within parentheses. Namely "(In particular,
> now and related strings are converted to a specific time value as soon
> as they are read.)".  Maybe it would be better to be more explicit
> there and mention that these are special values that the input
> function understands which are translated to actual timestamp values
> when the type's input function is called.  That could maybe be tied
> into the DEFAULT clause documentation to mention that the input
> function for constant values is called at DML time rather than DDL
> time.  That way, we're not adding these (unsustainable) special cases
> to the documentation.

This sounds like a reasonable approach to me for the
magic-input-values issue.  Do we want to do anything about
nextval()?  I guess if you hold your head at the correct
angle, that's also a magic-input-value issue, in the sense
that the question is when does regclass input get resolved.

			regards, tom lane