Re: Unexpected date conversion results

On Fri, Nov 21, 2025 at 4:55 PM Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:

> Laurenz Albe <laurenz(dot)albe(at)cybertec(dot)at> writes:
> > I dug into the git history, and it has been like that since commit
> b3506006b564
> > in 2002 (way before version 9.x). That commit fixed a bug that returned
> ten
> > time the correct reault (but still offset from the UTC epoch).
>
> I didn't bisect, but I get this in 9.1.24:
>
> regression=# set timezone = 'America/Los_Angeles';
> SET
> regression=# select to_timestamp(extract(epoch from current_date));
> to_timestamp
> ------------------------
> 2025-11-21 00:00:00-08
> (1 row)
>
> and this in 9.2.24:
>
> regression=# set timezone = 'America/Los_Angeles';
> SET
> regression=# select to_timestamp(extract(epoch from current_date));
> to_timestamp
> ------------------------
> 2025-11-20 16:00:00-08
> (1 row)
>
> regards, tom lane
>

I guess this reveals the age of the bit of code I was resurrecting, he says
while pulling out his Pg 8.4 release t-shirt. :)

After much more digging I found the relevant remark way back in the 9.2
release notes (https://www.postgresql.org/docs/release/9.2.0/)

Make EXTRACT(EPOCH FROM timestamp without time zone) measure the epoch from
local midnight, not UTC midnight (Tom Lane)

This change reverts an ill-considered change made in release 7.3. Measuring
from UTC midnight was inconsistent because it made the result dependent on
the timezone setting, which computations for timestamp without time zone
should not be. The previous behavior remains available by casting the input
value to timestamp with time zone.

Sorry for the goose chase.

-Steve