velvia commented on issue #686:
URL:
https://github.com/apache/arrow-datafusion/issues/686#issuecomment-876625232
@adamhopper personally I'd be OK with your recommendations, but some
thoughts:
- There is some interop considerations between `TIMESTAMP WITH TIMEZONE` ie
TimestampType(_, UTC) vs TimestampType(_, None). The reason is that so far
DataFusion has been generating `TimestampType(_, None)`. If this changes to
UTC, which makes sense as far as conventions go, then we need some way for
people with data with Timestamp(_, None) to be able to convert it over to (_,
UTC).
- I'm not sure it would be acceptable to throw an error at `isAdjustedToUTC
= false` as I'm sure people have Parquet files out there with this, and then
DataFusion/Arrow wouldn't be able to read it. But maybe it's OK if you give
people a way to cast / convert the timestamps over.
Also, I see your point about `to_timestamp()` having a timezone argument
being confusing. However there is a second use of `to_timestamp()` right
now, which is for conversion purposes, from other types to
Timestamp(resolution, tz). The reason it exists like this is because there is
no standard SQL/PG way to work with multiple timestamp resolutions, which are
required and supported by all Arrow implementations.
Thus, while `TO_TIMESTAMP('2021-01-01T00:00:00', 'America/Montreal')` might
be confusing, I believe the following would be more clear:
* `to_timestamp_millis(my_timestamp_col, 'UTC')` -> cast my_timestamp_col
from int or another timestamp resolution to millisecond resolution, and make
sure it has UTC timezone
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