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Thread: Getting yyyy-mm-dd 00:00:00 in an arbitrary time zone

Getting yyyy-mm-dd 00:00:00 in an arbitrary time zone

From
"Davidson, Robert"
Date:
<p><font face="Arial" size="2">I am trying to find out what the last full day of data for an arbitrary timezone
(generallynot the pg client's timezone). I get the max(timestamp), then would like to remove the time portion. Sounded
likea job for date_trunc, unfortunately date_trunc is not timezone aware:</font><p><font face="Arial" size="2">select
(date_trunc('day','2006-01-31 23:00:00-800' at time zone 'CST')) at time zone 'CST'</font><br /><font face="Arial"
size="2">2006-01-3122:00:00-08</font><p><font face="Arial" size="2">Since the client is in PST, the truncated date is
returnedas 2006-02-01 PST which is two hours before the desired time.</font><p><font face="Arial" size="2">extract is
slightlymore promising:</font><br /><font face="Arial" size="2">select extract(DAY from '2005-12-31 23:00:00-800' at
timezone 'CST')</font><br /><font face="Arial" size="2">1</font><p><font face="Arial" size="2">This returns the correct
day,so all I have to do is glue it back together in the right time zone:</font><br /><font face="Arial" size="2">select
to_timestamp(extract(YEARfrom '2005-12-31 23:00:00-800' at time zone 'CST')||'-'||</font><br />        <font
face="Arial"size="2">extract(MONTH from '2005-12-31 23:00:00-800' at time zone 'CST')||'-'||</font><br /><font
face="Arial"size="2">        extract(DAY from '2005-12-31 23:00:00-800' at time zone 'CST')||' 00:00:00 CST',
'YYYY-MM-DDHH:MI:SS TZ')</font><br /><font face="Arial" size="2">ERROR:  "TZ"/"tz" not supported</font><p><font
face="Arial"size="2">Has anyone solved this problem before?</font><p><font face="Arial" size="2">Many
thanks,</font><p><fontface="Arial" size="2">Robert</font><p><font face="Arial" size="2">Select version()</font><br
/><fontface="Arial" size="2">PostgreSQL 8.1.3 on i686-pc-linux-gnu, compiled by GCC 2.95.3</font>

Re: Getting yyyy-mm-dd 00:00:00 in an arbitrary time zone

From
Tom Lane
Date:
"Davidson, Robert" <robdavid@amazon.com> writes:
> I am trying to find out what the last full day of data for an arbitrary =
> timezone (generally not the pg client's timezone). I get the =
> max(timestamp), then would like to remove the time portion. Sounded like =
> a job for date_trunc, unfortunately date_trunc is not timezone aware:

> select (date_trunc('day', '2006-01-31 23:00:00-800' at time zone 'CST')) =
> at time zone 'CST'
> 2006-01-31 22:00:00-08

> Since the client is in PST, the truncated date is returned as 2006-02-01 =
> PST which is two hours before the desired time.

You're being quite unclear about what you want, but AFAICS the above
expression does exactly what you asked for.  Namely, you get a time that
is midnight in the CST zone and then is adjusted to your current
timezone for display.

Perhaps you could be more clear about why you don't like this result?
        regards, tom lane

Re: Getting yyyy-mm-dd 00:00:00 in an arbitrary time zone

From
"Davidson, Robert"
Date:
It does, doesn't it. And it does it just the way it is documented in 9.9.3 AT TIME ZONE table 9.27.

I was expecting it to be harder and didn't see I had figured out the right answer already - thanks!

Robert

-----Original Message-----
From: Tom Lane [mailto:tgl@sss.pgh.pa.us]
Sent: Friday, March 03, 2006 4:32 PM
To: Davidson, Robert
Cc: pgsql-sql@postgresql.org
Subject: Re: [SQL] Getting yyyy-mm-dd 00:00:00 in an arbitrary time zone

"Davidson, Robert" <robdavid@amazon.com> writes:
> I am trying to find out what the last full day of data for an
> arbitrary = timezone (generally not the pg client's timezone). I get
> the = max(timestamp), then would like to remove the time portion.
> Sounded like = a job for date_trunc, unfortunately date_trunc is not timezone aware:

> select (date_trunc('day', '2006-01-31 23:00:00-800' at time zone
> 'CST')) = at time zone 'CST'
> 2006-01-31 22:00:00-08

> Since the client is in PST, the truncated date is returned as
> 2006-02-01 = PST which is two hours before the desired time.

You're being quite unclear about what you want, but AFAICS the above expression does exactly what you asked for.
Namely,you get a time that is midnight in the CST zone and then is adjusted to your current timezone for display. 

Perhaps you could be more clear about why you don't like this result?
        regards, tom lane