Oddity with time zones.

Steve Rogerson <steve.pg@yewtc.demon.co.uk> writes:

# select (now());
now
-------------------------------
2017-04-03 11:57:09.891043+01
(1 row)

sjr_local1db=# select (now() AT TIME ZONE 'UTC');
timezone
----------------------------
2017-04-03 10:57:11.714571
(1 row)

sjr_local1db=# select (now() AT TIME ZONE 'UTC') AT TIME ZONE 'UTC';
timezone
-------------------------------
2017-04-03 11:57:14.088515+01
(1 row)

This makes no sense to me.

Looks perfectly fine from here. You're rotating a timestamp with time
zone (displayed in your local zone, evidently GMT+1) to a timestamp
without time zone expressed in UTC, and then back to a timestamp with time
zone. That round trip should be a no-op, barring weird corner cases.

I'd be the first to agree that the notation is pretty opaque --- why
use the same "operator" for both transformation directions? --- but
don't blame us, blame the SQL spec.

regards, tom lane

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