On Jun 7, 2007, at 16:07 , Steve Crawford wrote:
> On 8.2 I'm seeing an adjustment if the DST adjustment includes
> units of
> "day" or greater (ie. '1 day' and '1 day 01:00' get adjusted but '24
> hours' and '25 hours' do not).
>
> But PG doesn't follow the same rules in subtracting timestamptz values
> so operations involving timestamps and intervals are (sometimes) not
> reversible:
Right. It's only for timestamptz +/i interval.
> select timestamptz '2007-11-05' - timestamptz '2007-11-04';
>
> ?column?
> ----------------
> 1 day 01:00:00
It is a bit tricky. Datetime math is inherently so.
> select timestamptz '2007-11-04' + interval '1 day 01:00:00';
> ?column?
> ------------------------
> 2007-11-05 01:00:00-08
What PostgreSQL is doing behind the scenes is incrementing the date
2007-11-04 ahead 1 day and 1 hour. It treats months (and years),
days, and time separately.
Michael Glaesemann
grzm seespotcode net
