Re: Returning timestamp with timezone at specified timezone irrespective of client timezone

On 9/27/20 4:16 PM, aNullValue (Drew Stemen) wrote:
> Hello,
>
> I've attempted to obtain help with this problem from several other places,
> but numerous individuals recommended I ask this mailing list.
>
> What I need is for the ability to return a timestamp with timezone, using
> the UTC offset that corresponds to a column-defined timezone, irrespective
> of the client/session configured timezone.
>
> I have three columns in a table:
> Timezone: 'US/Eastern'
> Date: 2020-10-31
> Time: 08:00
>
> The output I'm able to find includes these possibilities:
> '2020-10-31 08:00:00'
> '2020-10-31 12:00:00+00'
>
> Whereas what I actually need is:
> '2020-10-31 08:00:00-05'
>
> Using the postgresql session-level timezone configuration won't work
> because I need multiple timezones to be handled in a single set.
>
> Example code follows. I'm not using to_char in the examples as I likely
> would in the production code, but I haven't found any way that it could be
> helpful here regardless.
>
[snip]
>
> id |  timezone  | loc_date  | loc_time |         tswtz          |       tswotz
> ----+------------+------------+----------+------------------------+---------------------
>   7 | US/Central | 2020-10-31 | 08:00    | 2020-10-31 13:00:00+00 |
> 2020-10-31 08:00:00
>   8 | US/Central | 2020-11-03 | 08:00    | 2020-11-03 14:00:00+00 |
> 2020-11-03 08:00:00
>   5 | US/Eastern | 2020-10-31 | 08:00    | 2020-10-31 12:00:00+00 |
> 2020-10-31 08:00:00
>   6 | US/Eastern | 2020-11-03 | 08:00    | 2020-11-03 13:00:00+00 |
> 2020-11-03 08:00:00
> (4 rows)
>
> What I actually need is, in example id=7, '2020-10-31 08:00:00-05'.
>
> Is this even possible? Several people have proposed that I write a custom
> function to do this on a per-row basis, which... I suppose I can do... I'm
> just blown away that this isn't something that just works "out of the box".
>

Are you really asking what the TZ offset was on a specific date (Like DST or
not)?

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