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Message-ID: <438f84e1-52ff-410e-8e33-03029f04927a@aklaver.com>
Date: Fri, 21 Nov 2025 16:52:40 -0800
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Subject: Re: Unexpected date conversion results
From: Adrian Klaver <adrian.klaver@aklaver.com>
To: Steve Crawford <scrawford@pinpointresearch.com>,
 PG-General Mailing List <pgsql-general@postgresql.org>
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 <fd3ad9cc-50da-47a4-8177-3915ad7186bf@aklaver.com>
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On 11/21/25 16:38, Adrian Klaver wrote:
> On 11/21/25 16:09, Steve Crawford wrote:
>> Either there is a bug in my understanding or one in PostgreSQL. I 
>> expect a date value to follow the current time zone setting and be 
>> interpreted as midnight at the start of the given date. In many cases 
>> it does. Shown below are the postgresql.conf settings and the psql 
>> client settings showing the time zone to be America/Los_Angeles:
>>
>> postgresql.conf:
>> log_timezone = 'America/Los_Angeles'
>> timezone = 'America/Los_Angeles'
>>
>> Client time zone setting:
>>
>>     steve=> show timezone;
>>            TimeZone
>>     ---------------------
>>       America/Los_Angeles
>>
>>
> 
>> However, extracting the epoch from current_date returns 4pm the prior 
>> day (i.e. 2025-11-21 00:00:00-00), in other words midnight 2025-11-21 
>> UTC which seems to be inconsistent behavior:
> 
> 
> https://www.postgresql.org/docs/current/functions- 
> datetime.html#FUNCTIONS-DATETIME-EXTRACT
> 
> "epoch
> 
>      For timestamp with time zone values, the number of seconds since 
> 1970-01-01 00:00:00 UTC (negative for timestamps before that); for date 
> and timestamp values, the nominal number of seconds since 1970-01-01 
> 00:00:00, without regard to timezone or daylight-savings rules; for 
> interval values, the total number of seconds in the interval
> "
> 
> So epoch is in UTC which is confirmed by below.
>>
>>     steve=> select to_timestamp(extract(epoch from current_date));
>>            to_timestamp
>>     ------------------------
>>       2025-11-20 16:00:00-08
> 
> If you want it to work(I am in  'America/Los_Angeles' also):
> 
> select to_timestamp(extract(epoch from current_date)) at time zone  'UTC';
> 
>       timezone
> ---------------------
>   2025-11-21 00:00:00

Or something like:

select extract(epoch from current_date);
   extract
------------
  1763683200

select to_timestamp(extract(epoch from current_date));
       to_timestamp
------------------------
  2025-11-20 16:00:00-08


select extract(epoch from current_date::timestamptz);
       extract
-------------------
  1763712000.000000

select to_timestamp(extract(epoch from current_date::timestamptz));
       to_timestamp
------------------------
  2025-11-21 00:00:00-08

Where the latter does the rotation to the TimeZone setting via 
::timestamptz and you get 28,800 second(8 hr) difference and a returned 
timestamptz that is correct for the TimeZone.


> 
> 
>> There was a time, like version 9-dot-something, when the above queries 
>> performed as expected returning midnight in the current time zone but 
>> I haven't been able to find a change document indicating this as an 
>> expected change.
> 
> I don't remember that, but as the gray content of the hair increases the 
> memory is less solid:)
> 
>>
>> -Steve
> 
> 


-- 
Adrian Klaver
adrian.klaver@aklaver.com