Обсуждение: Time AT TIME ZONE: false result using offset instead of time zone name

Hi,
I am living in the Central European Time (CET == GMT+1)

SELECT CURRENT_TIMESTAMP ;

now
timestamp with time zone
----------------------------
2014-02-11 08:21:52.83588+01

And I want this without time zone but also for my own time zone (checking AT
TIME ZONE); sure, I get it correct... the same...

SELECT CURRENT_TIMESTAMP AT TIME ZONE 'CET';

timezone
timestamp without time zone
----------------------------
2014-02-11 08:22:39.586382

But it would be easier to ask a specific time offset (got from a client
around the world), so for me +01 hour:

SELECT CURRENT_TIMESTAMP AT TIME ZONE 'UTC+01';

timezone
timestamp without time zone
---------------------------
2014-02-11 06:23:07.043479

!!! Two hours earlyer, one hour to the east (Azores), not to the west of
Greenwich.
To get my time one hour west from Greenwich I have to ask:

SELECT CURRENT_TIMESTAMP AT TIME ZONE 'UTC-01';

Is this inverse calculation intently?

Thank you!
Regards, Rawi




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On 02/10/2014 11:54 PM, rawi wrote:
> Hi,
> I am living in the Central European Time (CET == GMT+1)
>
> SELECT CURRENT_TIMESTAMP ;
>
> now
> timestamp with time zone
> ----------------------------
> 2014-02-11 08:21:52.83588+01
>
> And I want this without time zone but also for my own time zone (checking AT
> TIME ZONE); sure, I get it correct... the same...
>
> SELECT CURRENT_TIMESTAMP AT TIME ZONE 'CET';
>
> timezone
> timestamp without time zone
> ----------------------------
> 2014-02-11 08:22:39.586382
>
> But it would be easier to ask a specific time offset (got from a client
> around the world), so for me +01 hour:
>
> SELECT CURRENT_TIMESTAMP AT TIME ZONE 'UTC+01';
>
> timezone
> timestamp without time zone
> ---------------------------
> 2014-02-11 06:23:07.043479
>
> !!! Two hours earlyer, one hour to the east (Azores), not to the west of
> Greenwich.
> To get my time one hour west from Greenwich I have to ask:
>
> SELECT CURRENT_TIMESTAMP AT TIME ZONE 'UTC-01';
>
> Is this inverse calculation intently?

Yes.

http://www.postgresql.org/docs/9.3/interactive/datatype-datetime.html#DATATYPE-TIMEZONES

8.5.3. Time Zones

.. Another issue to keep in mind is that in POSIX time zone names, 
positive offsets are used for locations west of Greenwich. Everywhere 
else, PostgreSQL follows the ISO-8601 convention that positive timezone 
offsets are east of Greenwich

>
> Thank you!
> Regards, Rawi
>
>
>
>
> --
> View this message in context:
http://postgresql.1045698.n5.nabble.com/Time-AT-TIME-ZONE-false-result-using-offset-instead-of-time-zone-name-tp5791371.html
> Sent from the PostgreSQL - sql mailing list archive at Nabble.com.
>
>


-- 
Adrian Klaver
adrian.klaver@gmail.com

Adrian Klaver-3 wrote
>>On 02/10/2014 11:54 PM, rawi wrote:
>>[...]
>> SELECT CURRENT_TIMESTAMP AT TIME ZONE 'UTC+01';
>>
>> timezone
>> timestamp without time zone
>> ---------------------------
>> 2014-02-11 06:23:07.043479
>>
>> !!! Two hours earlyer, one hour to the east (Azores), not to the west of
>> Greenwich.
>> To get my time one hour west from Greenwich I have to ask:
>>
>> SELECT CURRENT_TIMESTAMP AT TIME ZONE 'UTC-01';
>>
>> Is this inverse calculation intently?
> 
> Yes.
> 
> http://www.postgresql.org/docs/9.3/interactive/datatype-datetime.html#DATATYPE-TIMEZONES
> 
> 8.5.3. Time Zones
> 
> .. Another issue to keep in mind is that in POSIX time zone names, 
> positive offsets are used for locations west of Greenwich. Everywhere 
> else, PostgreSQL follows the ISO-8601 convention that positive timezone 
> offsets are east of Greenwich

Oh... oh... Disconcerting... I've just learned, that even javascript is
returning negative offsets for western situated browsers...

Thank you!
Regards, Rawi




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On 02/12/2014 12:24 AM, rawi wrote:
> Adrian Klaver-3 wrote
>>> On 02/10/2014 11:54 PM, rawi wrote:
>>> [...]
>>> SELECT CURRENT_TIMESTAMP AT TIME ZONE 'UTC+01';
>>>
>>> timezone
>>> timestamp without time zone
>>> ---------------------------
>>> 2014-02-11 06:23:07.043479
>>>
>>> !!! Two hours earlyer, one hour to the east (Azores), not to the west of
>>> Greenwich.
>>> To get my time one hour west from Greenwich I have to ask:
>>>
>>> SELECT CURRENT_TIMESTAMP AT TIME ZONE 'UTC-01';
>>>
>>> Is this inverse calculation intently?
>>
>> Yes.
>>
>> http://www.postgresql.org/docs/9.3/interactive/datatype-datetime.html#DATATYPE-TIMEZONES
>>
>> 8.5.3. Time Zones
>>
>> .. Another issue to keep in mind is that in POSIX time zone names,
>> positive offsets are used for locations west of Greenwich. Everywhere
>> else, PostgreSQL follows the ISO-8601 convention that positive timezone
>> offsets are east of Greenwich
>
> Oh... oh... Disconcerting... I've just learned, that even javascript is
> returning negative offsets for western situated browsers...

Welcome to the wacky world of time, it is all relative:) The choices are 
handle everything as UTC until you present to the end user or use actual 
timezones, for example, America/Los_Angeles. To illustrate, in your 
original post you said:

"But it would be easier to ask a specific time offset (got from a client
around the world), so for me +01 hour"

Do you know if that offset supplied by the client was POSIX or ISO in 
its sign?

>
> Thank you!
> Regards, Rawi
>
>
>



-- 
Adrian Klaver
adrian.klaver@gmail.com

Adrian Klaver-3 wrote
> Welcome to the wacky world of time, it is all relative:) The choices are 
> handle everything as UTC until you present to the end user or use actual 
> timezones, for example, America/Los_Angeles. To illustrate, in your 
> original post you said:
> 
> "But it would be easier to ask a specific time offset (got from a client
> around the world), so for me +01 hour"
> 
> Do you know if that offset supplied by the client was POSIX or ISO in 
> its sign?

The (playing) question was: how would I get the time zone of a browser
somewhere unknown on earth?

And the found javascript solution would return the difference between GMT
and localtime in minutes, so for me west from Greenwich a negative integer.

Please save the following in a html file eg. "time_offset.html" and load it
in your browser:





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On 02/12/2014 07:29 AM, rawi wrote:
> Adrian Klaver-3 wrote
>> Welcome to the wacky world of time, it is all relative:) The choices are
>> handle everything as UTC until you present to the end user or use actual
>> timezones, for example, America/Los_Angeles. To illustrate, in your
>> original post you said:
>>
>> "But it would be easier to ask a specific time offset (got from a client
>> around the world), so for me +01 hour"
>>
>> Do you know if that offset supplied by the client was POSIX or ISO in
>> its sign?
>
> The (playing) question was: how would I get the time zone of a browser
> somewhere unknown on earth?
>
> And the found javascript solution would return the difference between GMT
> and localtime in minutes, so for me west from Greenwich a negative integer.
>
> Please save the following in a html file eg. "time_offset.html" and load it
> in your browser:


I do not see the code, so I can not test.

>
>
>
>
>



-- 
Adrian Klaver
adrian.klaver@gmail.com

On 02/12/2014 07:29 AM, rawi wrote:
> Adrian Klaver-3 wrote
>> Welcome to the wacky world of time, it is all relative:) The choices are
>> handle everything as UTC until you present to the end user or use actual
>> timezones, for example, America/Los_Angeles. To illustrate, in your
>> original post you said:
>>
>> "But it would be easier to ask a specific time offset (got from a client
>> around the world), so for me +01 hour"
>>
>> Do you know if that offset supplied by the client was POSIX or ISO in
>> its sign?
>
> The (playing) question was: how would I get the time zone of a browser
> somewhere unknown on earth?
>
> And the found javascript solution would return the difference between GMT
> and localtime in minutes, so for me west from Greenwich a negative integer.
>
> Please save the following in a html file eg. "time_offset.html" and load it
> in your browser:


I am on the US Pacific Coast so my current timezone is PST, UTC-8 ISO

So using javascript in my browser:

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Date/getTimezoneOffset


var offset = new Date().getTimezoneOffset();

offset = 480

480 minutes/60 minutes = 8 hours

Which tracks with the above link:

"The time-zone offset is the difference, in minutes, between UTC and 
local time. Note that this means that the offset is positive if the 
local timezone is behind UTC and negative if it is ahead."

and also the POSIX offset. You just have to remember to invert sign for 
your local timezone when doing the AT TIMEZONE if you use the POSIX method.

Of course you are counting on the client having their environment set up 
correctly.


>
>
>
>
>


-- 
Adrian Klaver
adrian.klaver@gmail.com