waitingkuo commented on issue #4106:
URL:
https://github.com/apache/arrow-datafusion/issues/4106#issuecomment-1304498803
> @waitingkuo thank you for your clear communication as always! You have the
most reviewable PRs and issues I've seen 😄 .
❤️
>
> The issue looks good to me, but I would propose tackling in stages:
>
> 1. Allow things like `set time zone to '+08:00';` as described
> 2. Allow `set time zone to 'US/Mountain';` or `set time zone to
'US/Denver';` or `set time zone to 'MT';`
>
> This is due to the extra complication of what to do when someone does a
`select TO_TIMESTAMP('2022-11-06T01:30:00');` and the server timezone is
'US/Mountain' and there are two distinct 1:30AMs one in MDT and one in MST. Do
we know what postgres does here? The only sensible thing I can think to do is
fail the query with an error.
PostgreSQL's `to_timestamp` ouputs `timestamp with time zone`
https://www.postgresql.org/docs/current/functions-formatting.html
```bash
to_timestamp ( text, text ) → timestamp with time zone
Converts string to time stamp according to the given format.
to_timestamp('05 Dec 2000', 'DD Mon YYYY') → 2000-12-05 00:00:00-05
```
```bash
willy=# set timezone to 'America/Denver';
SET
willy=# select to_timestamp('05 Dec 2000', 'DD Mon YYYY');
to_timestamp
------------------------
2000-12-05 00:00:00-07
(1 row)
```
it shows the fixed offset timezone. i think there's no ambiguity in this
approach.
The `TO_TIMESTAMP` for datafusion for now outputs `Timestamp<TimeUnit,
None>`.
https://github.com/apache/arrow-datafusion/blob/6d00bd990ce5644181ad1549a6c70c8406219070/datafusion/expr/src/function.rs#L206-L220
I think it will make more sense if these `TO_TIMESTSMP_XX` functions change
the signatures to Timestamp with Timezone. This is in my backlog as well . I
was working on #2979 to align `TO_TIMESTAMP` to Postgrseql's but found that we
don't have timezone support. So I moved the focus to finish the time zone
support (from sqlparser, arrow-rs, and finally datafusion 😃 )
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