westonpace edited a comment on issue #686:
URL:
https://github.com/apache/arrow-datafusion/issues/686#issuecomment-884535402
Aside: this case `to_timestamp('2021-07-20', 'UTC')` could be ambiguous if
the server time zone happens to be in a DST shift.
> I think this is consistent with what @westonpace has in his table
Then I think what you have proposed matches (as best I can tell) the
recently agreed upon spec so that is all good. Usability-wise, I don't know,
but I'll admit I don't have much stake in a usability decision (I'm more
worried about interoperability). So take this next paragraph with a grain of
salt :laughing:
It feels to me like `to_timestamp` is doing two steps. First, it is
converting to a string to a Timestamp (respecting the offset in the string, if
any). Second, it is "reinterpret" casting (schema only change) that timestamp
to the desired local/instant semantics. I'd personally prefer something that
breaks things into two steps if needed.
Example | One Step Type | Two Step Equivalent | Two Step Type
-- | -- | -- | --
to_timestamp('1970-01-01') | Timestamp(Nanoseconds, None) |
reinterpret_zone(to_timestamp('1970-01-01'), None) | Timestamp(Nanoseconds,
None)
to_timestamp('1970-01-01+00:00') | Timestamp(Nanoseconds, Utc) |
reinterpret_zone(to_timestamp('1970-01-01+00:00'), None) |
Timestamp(Nanoseconds, None)
to_timestamp('1970-01-01+01:00') | Timestamp(Nanoseconds, +01:00) |
reinterpret_zone(to_timestamp('1970-01-01+01:00'), None) |
Timestamp(Nanoseconds, None)
to_timestamp('1970-01-01', 'UTC') | Timestamp(Nanoseconds, None) |
reinterpret_zone(to_timestamp('1970-01-01'), 'UTC') | Timestamp(Nanoseconds,
Utc)
to_timestamp('1970-01-01+00:00', 'UTC') | Timestamp(Nanoseconds, Utc) |
reinterpret_zone(to_timestamp('1970-01-01+00:00', 'UTC'), 'Utc') |
Timestamp(Nanoseconds, Utc)
to_timestamp('1970-01-01+01:00', 'UTC') | Timestamp(Nanoseconds, +01:00) |
reinterpret_zone(to_timestamp('1970-01-01+01:00'), 'UTC') |
Timestamp(Nanoseconds, Utc)
This would change the meaning of the fourth row so it would have the value 0.
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