Re: unexpected behavior in combining timestamps with times zone and intervals

Charles Seaton <cseaton(at)stccmop(dot)org> writes:
> Thanks for your response. I am wondering whether it is postgres 8.2.5
> that resolves the problem or your time zone setting.

This behavior changed in PG 8.1. Per the release notes:

* Add a separate day field to type interval so a one day interval can be
distinguished from a 24 hour interval (Michael Glaesemann)

Days that contain a daylight saving time adjustment are not 24 hours
long, but typically 23 or 25 hours. This change creates a conceptual
distinction between intervals of "so many days" and intervals of "so
many hours". Adding 1 day to a timestamp now gives the same local time
on the next day even if a daylight saving time adjustment occurs
between, whereas adding 24 hours will give a different local time when
this happens. For example, under US DST rules:

'2005-04-03 00:00:00-05' + '1 day' = '2005-04-04 00:00:00-04'
'2005-04-03 00:00:00-05' + '24 hours' = '2005-04-04 01:00:00-04'

regards, tom lane