waitingkuo commented on issue #3664:
URL: https://github.com/apache/arrow-rs/issues/3664#issuecomment-1420335167
> @tustvold sorry probably I have expressed not very clear. The entire idea
is to cast user provided Utf8 value to Timestamp with timezone like
>
> ```
> select "2023-01-01 04:05:06.789-8"::timestamptz union all
> select "2023-01-01 04:05:06.789-7"::timestamptz
> ```
>
> In Datafusion such transformation happens through arrow-rs `cast` function
which has single target datatype , in this specific case I believe it would be
`DataType::Timestamp(TimeUnit::Nanosecond, Something)` where is Something is
not very clear for me. Presumably we can use `+00:00` or `None`, I'm struggling
if we can lose precision in this case.
I think casting to timestamptz should return the same time zone (the one
shown in `SHOW TIME ZONE`) in the same query.
i'm in UTC+8
in postgresql, `select '2023-01-01 04:05:06.789-8'::timestamptz` returns
timestamptz in UTC+8
```bash
willy=# select '2023-01-01T04:05:06.789-8'::timestamptz;
timestamptz
----------------------------
2023-01-01 20:05:06.789+08
(1 row)
```
```bash
willy=# select '2023-01-01 04:05:06.789-7'::timestamptz;
timestamptz
----------------------------
2023-01-01 19:05:06.789+08
(1 row)
```
so in your query, the union return +8 time zone (my current time zone) for
me in postgresql.
I think we could consider either fix it to +00:00 or current timezone
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