Re: Inconsistent 'at time zone' conversion

Thank you  for your answers David G. Johnston and Tom Land. That is much more clear now.

Yet, there is one tiny thing left:

1. select TIMESTAMP WITH TIME ZONE '2004-10-19 10:23:54+03' at time zone 'America/Denver';

  2004-10-19 01:23:54

2. select TIMESTAMP WITH TIME ZONE '2004-10-19 10:23:54+03' at time zone 'UTC+7';

  2004-10-19 00:23:54

3. select TIMESTAMP WITH TIME ZONE '2004-10-19 10:23:54+03' at time zone 'Europe/Moscow';
  2004-10-19 11:23:54

4. select TIMESTAMP WITH TIME ZONE '2004-10-19 10:23:54+03' at time zone 'UTC-3';

  2004-10-19 10:23:54

The outputs of the 1st and the 2nd queries should be the same because "+/-" works opposite of ISO - 8601. Same thing should apply to query 3rd and 4th.

When I try following queries they give exactly the same output.

select now()::timestamp with time zone  at time zone 'America/Denver';

select now()::timestamp with time zone  at time zone 'UTC+7';

So, it should be related to the date. Yet, as you can see '2004-10-19 10:23:54+03' is nearly the same time of the year 18 years and 4 months ago. So, the same DST rules should apply, but it does not. There is 1 hour difference between query 1st and 2nd, also query 3rd and 4th.

In order to check DST for the specified timestamp: https://www.timeanddate.com/worldclock/converter.html?iso=20040219T072300&p1=tz_gmt&p2=75

What could be the reason for this?

Thanks!

Umut Tekin