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From: "M. Strobel" <sorry_no_mail_here@nowhere.dee>
Newsgroups: comp.databases.postgresql
Subject: Re: timestamp and time zone
Date: Sat, 30 Apr 2011 17:58:37 +0200
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Am 30.04.2011 13:15, schrieb Jasen Betts:
> On 2011-04-28, M. Strobel <sorry_no_mail_here@nowhere.dee> wrote:
>> Hi,
>>
>> I did not quite understand the use case of timestamp with time zone.
>>
>> When do you need 'with time zone'?
> 
> it's best to use it when you are dealing with real events that happen
> at a specific instant
> 
>> My tests show you can
>> calculate other time zones time easily from a timestamp without
>> time zone.
> 
>> Is timestamp internally stored normalized to utc, and calculated
>> to client time zone? Or to server time zone?
> 
> timestamp with timezone is internally stored as a UTC timestamp
> no zone information is stored. So '2011-04-30 23:02:39.296282+12'
> is actually stored as '2011-04-30 11:02:39.296282 UTC'.  (I know 
> it says "with timezone" on the label - postgresql fakes it )
> (actually it's stored as a number, not as a string)
> 
> When it's retreived it will be translated to the best guess zone
> apropriate for the user (using the server operating system's timezone
> database)
> 
> timestamp is internally stored with no zone translation so 
> '2011-04-30 23:02:39.296282' will look the same whatever 
> the user uses for their timezone. (different datestyle
> settings can effect the date part however)
> 
I see. So there is no automatic translation 'without time zone',
but if you ask the system to translate it to another time zone it
does so assuming local time.

Thanks, I thought it was too much work to set up tests within
different time zones...

/Str.