adamhooper edited a comment on issue #686:
URL:
https://github.com/apache/arrow-datafusion/issues/686#issuecomment-884485767
> to_timestamp('1970-01-01', 'UTC') `Timestamp(Nanoseconds, Utc)`
5*3600000000000 (5 hour of nanoseconds) **assuming code was run on a computer
set to EDT, UTC-5:00**
Oh, I see -- this is existing behavior. But then, does existing behavior
define a different result for row 1?
https://github.com/apache/arrow-datafusion/blob/5900b4c6829b0bdbe69e1f95fb74e935bc8f33d4/datafusion/src/physical_plan/datetime_expressions.rs#L85
In my view, if the existing behavior has to stay, it has to stay; but if it
_doesn't_ have to stay, then as a user I'd feel much more comfortable if
DataFusion didn't expose the server's timezone -- or at least made it a session
variable, as Postgres does.
Note that we're up to _four_ timezones in every call to `TO_TIMESTAMP()`:
* `NULL`: "localtime" the Arrow concept -- calendar-date-plus-wall-time
* `UTC`
* The input-string timezone offset
* DataFusion server's "local timezone" (distinct from Arrow's "local time",
and presumably unknown to my users)
My use case is to run custom SQL from the general public. I realize I can
use environment variables to force DataFusion's "server timezone" to be UTC;
but that doesn't negate the learning curve.
Postgres has the same complexity. Its syntax:
* `SELECT timestamp_with_time_zone AT TIME ZONE 'America/Eastern'` =>
converts UTC to localtime
* `SELECT timestamp_with_time_zone::TIMESTAMP` => converts UTC to
session-timezone localtime
* `SELECT timestamp_without_time_zone AT TIME ZONE 'America/Eastern' =>
converts localtime to UTC
* `SELECT timestamp_without_time_zone::TIMESTAMPTZ` => converts localtime to
UTC using session-timezone localtime
... and I'll bet most Postgres misunderstand these concepts for years until
they figure it out.
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