Обсуждение: UTC-6 or UTC+6?

I'm a little confused by trying to get the time at a different
timezone, formerly UTC-6:

template1=# select '2019-10-22 16:00:00' at time zone 'Europe/Rome' as my_time
, '2019-10-22 16:00:00' at time zone 'America/Denver' as what_should_be,
'2019-10-22 16:00:00' at time zone 'UTC-6' as utc_minus_6,
'2019-10-22 16:00:00' at time zone 'UTC+6' as utc_plus_6;
-[ RECORD 1 ]--+--------------------
my_time        | 2019-10-22 16:00:00
what_should_be | 2019-10-22 08:00:00
utc_minus_6    | 2019-10-22 20:00:00
utc_plus_6     | 2019-10-22 08:00:00


Now, the denver time should be 8:00, which is what is reported as
UTC+6, but as far as I know Denver is UTC-6 (in daylight saving). What
am I missing here?

Thanks,
Luca

Luca Ferrari <fluca1978@gmail.com> writes:
> template1=# select '2019-10-22 16:00:00' at time zone 'Europe/Rome' as my_time
> , '2019-10-22 16:00:00' at time zone 'America/Denver' as what_should_be,
> '2019-10-22 16:00:00' at time zone 'UTC-6' as utc_minus_6,
> '2019-10-22 16:00:00' at time zone 'UTC+6' as utc_plus_6;
> -[ RECORD 1 ]--+--------------------
> my_time        | 2019-10-22 16:00:00
> what_should_be | 2019-10-22 08:00:00
> utc_minus_6    | 2019-10-22 20:00:00
> utc_plus_6     | 2019-10-22 08:00:00

> Now, the denver time should be 8:00, which is what is reported as
> UTC+6, but as far as I know Denver is UTC-6 (in daylight saving). What
> am I missing here?

Timezone names of that form are interpreted per the POSIX standard,
which uses positive for west-of-Greenwich, unlike the ISO standard
which uses the opposite sign.  See

https://www.postgresql.org/docs/current/datatype-datetime.html#DATATYPE-TIMEZONES

            regards, tom lane