On 04/02/2015 11:01 AM, Steve Crawford wrote:
On 04/02/2015 10:34 AM, David G. Johnston wrote:
On Thu, Apr 2, 2015 at 10:27 AM, James Cloos <cloos@xxxxxxxxxxx
<mailto:cloos@xxxxxxxxxxx>>wrote:
>>>>> "SC" == Steve Crawford <scrawford@xxxxxxxxxxxxxxxxxxxx
<mailto:scrawford@xxxxxxxxxxxxxxxxxxxx>> writes:
...
What I haven't determined is why converting back is off by 21600
seconds.
What timezone is your server set to - and/or the client requesting
the calculation?
I haven't looked to see if that is a plausible explanation but if
you are +/- 6hrs from UTC...
David J.
I was actually just looking at the microseconds being off. Now I'm
curious again and haven't been able to come up with a plausible
explanation. My client and server are in America/Pacific time zone. What
I've seen so far:
First, there appears to be some lingering automatic casting:
select 'epoch';
?column?
----------
epoch
select 'epoch' at time zone 'UTC';
timezone
---------------------
1970-01-01 00:00:00
In the Pacific time zone, I should be -07 from UTC but if I strip down
James' statement to the following the result shows as -08, not -07:
Which would be correct for 12/31/1969 as standard time was in effect.
select 'epoch'::timestamptz;
timestamptz
------------------------
1969-12-31 16:00:00-08
Which we can see is correct:
select '1969-12-31 16:00:00-08'::timestamptz at time zone 'UTC';
timezone
---------------------
1970-01-01 00:00:00
But something gets crossed up when we add a couple calculations:
select (now() - (now() - 'epoch')) ;
?column?
------------------------
1969-12-31 17:00:00-08
Now you are mixing intervals and timestamps, something I try to avoid
because of all the converting that goes on.
Now we are off by an hour:
select (now() - (now() - 'epoch')) at time zone 'UTC';
timezone
---------------------
1970-01-01 01:00:00
select (now()::timestamp without time zone - (now()::timestamp without
time zone - 'epoch'));
?column?
---------------------
1970-01-01 00:00:00
Or:
test=> select now() - extract('epoch' from (now() -
'epoch'::timestamptz)) * interval '1 sec';
?column?
------------------------
1969-12-31 16:00:00-08
That's all I've discovered so far but I have to run to a meeting.
Cheers,
Steve
--
Adrian Klaver
adrian.klaver@xxxxxxxxxxx
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