From: Tom Lane <tgl@sss.pgh.pa.us>
To: fcaldasdesou@bloomberg.net
cc: pgsql-bugs@lists.postgresql.org
Subject: Re: BUG #18445: date_part / extract range for hours do not match
 documentation
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References: <18445-2bdf6f3c730abe6d@postgresql.org>
Comments: In-reply-to PG Bug reporting form <noreply@postgresql.org>
	message dated "Tue, 23 Apr 2024 10:10:25 -0000"
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Date: Tue, 23 Apr 2024 10:39:53 -0400
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PG Bug reporting form <noreply@postgresql.org> writes:
> In https://www.postgresql.org/docs/8.1/functions-datetime.html

It would be a good idea to look at versions of the documentation
that aren't so many years obsolete.  8.1 has been EOL since 2010.

> We say that EXTRACT() should return a number between 0-23 for hours

What it says now is

        The hour field (0-23 in timestamps, unrestricted in intervals)

(This wording is currently only visible at
https://www.postgresql.org/docs/devel/functions-datetime.html#FUNCTIONS-DA=
TETIME-EXTRACT
but it will propagate into the website's copies of still-maintained
branches at our next quarterly updates.)

> The function seems to also return 24 in some cases eg:
> SELECT date_part('hour', cast('24:00:00.00' as time))::int
> Could we update the documentation or modify the function so that it wrap=
s 24
> back to 0 hours?

That edge case for type "time" is deliberate; see the definition
of that type in table 8.9 here:

https://www.postgresql.org/docs/devel/datatype-datetime.html

I don't really feel a need to clutter the documentation for EXTRACT()
still more by mentioning it there, especially since the current
wording is not wrong, just silent about that detail.

			regards, tom lane