[GitHub] [arrow-datafusion] westonpace edited a comment on issue #686: Specific timezone support for `to_timetamp*()`

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westonpace edited a comment on issue #686:
URL: https://github.com/apache/arrow-datafusion/issues/686#issuecomment-884452349


   Does this seem correct?
   
   
   
   Example | Output Arrow Type | Value | Output when printed
   -- | -- | -- | --
   to_timestamp('2021-07-20') | Timestamp(Nanoseconds, None) | nanos since unix epic until 2021-07-20 local time | 2021-07-20T00:00:00
   to_timestamp('2021-07-20+00:00') | Timestamp(Nanoseconds, None) | nanos since unix epic until 2021-07-20 UTC | 2021-07-20T00:00:00
   to_timestamp('2021-07-20+01:00') | Timestamp(Nanoseconds, None) | nanos since unix epic until 2021-07-20 UTC+1 | 2021-07-19T23:00:00
   to_timestamp('2021-07-20', 'UTC') | Timestamp(Nanoseconds, Utc) | nanos since unix epic until 2021-07-20 local time | 2021-07-19T00:00:00Z
   to_timestamp('2021-07-20+00:00', 'UTC') | Timestamp(Nanoseconds, Utc) | nanos since unix epic until 2021-07-20 UTC | 2021-07-20T00:00:00Z
   to_timestamp('2021-07-20+01:00', 'UTC') | Timestamp(Nanoseconds, Utc) | nanos since unix epic until 2021-07-20 UTC | 2021-07-20T23:00:00Z
   
   I think the one most interesting to me is row 4 so double check that one (also not the presence/absence of a trailing Z to indicate local time or not).
   
   By "output when printed" I mean what an implementation would get if it tried to force the value into an ISO-8601 string.
   
   Just a few extra thoughts...
   
   Does `to_timestamp` only accept offsets in the strings (e.g. `+01:00` and not tzdata strings or things like `MST`)?  For reference, ISO-8601 only deals with offsets.
   
   Will Rust ever generate an Output Arrow Type with a time zone string (e.g. MST)?
   
   My point with the last two questions is that offset conversions aren't too bad if you aren't handling tzdata strings.  Once you do then you need a timezone database which is a bit of a pain but solvable.  The C++ impl recently added compute kernels which rely on a timezone database and it's a non-trivial effort.  @rok has been spearheading this effort so you might reach out if you go down this road.
   
   


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