On 5/22/21 3:09 AM, Peter J. Holzer wrote:
On 2021-05-19 06:57:13 -0700, Adrian Klaver wrote:
On 5/18/21 11:31 PM, Bryn Llewellyn wrote:
This seems to be at odds with what section “8.5.3. Time Zones” at
https://www.postgresql.org/docs/current/datatype-datetime.html#DATATYPE-TIMEZONES <https://www.postgresql.org/docs/current/datatype-datetime.html#DATATYPE-TIMEZONES>
says:
«
A time zone abbreviation, for example PST. Such a specification merely
defines a particular offset from UTC, in contrast to full time zone
names which can imply a set of daylight savings transition rules as
well. The recognized abbreviations are listed in
the pg_timezone_abbrevs view (see Section 51.91). You cannot set the
configuration parameters TimeZone or log_timezone to a time zone
abbreviation, but you can use abbreviations in date/time input values
and with the AT TIME ZONE operator.
»
This claims (as I read it) that a time zone abbreviation uniquely
determines an offset from UTC.
It says no such thing
Maybe that's the inherent ambiguity of the English language, but to me
"Such a specification defines a particular offset from UTC" does imply a
one-to-one mapping from abbreviation to offset.
As your later post points out the reality is a given abbreviation has
only one offset, but an offset may have many abbreviations.
and would be lying if it did.
As far as pg_timezone_abbrevs is concerned, it is correct. abbrev is
unique in that view:
1) Go to Postgres cluster and in ~/share/timezonesets search in
Defaults.txt for the word C(c)onflict.
2)Then go here
https://www.postgresql.org/docs/current/datetime-config-files.html and
see how the below query could be made to change if someone is not aware
of 1).
More below.
hjp=> select abbrev, count(*) from pg_timezone_abbrevs group by 1 having count(*) > 1;
╔════════╤═══════╗
║ abbrev │ count ║
╟────────┼───────╢
╚════════╧═══════╝
(0 rows)
(at least in PostgreSQL 11.12)
It is not true in "the real world", where different time zones may use
the same abbreviation. But that isn't what the paragraph is about.
~/share/timezonesets encompasses the 'real world'.
What it is saying that, for example, the timezone America/Los_Angeles has
two timezone abbreviations PDT(what I'm currently in) and PST. If you use an
abbreviation you don't get the DST transition rules that a full timezone
name has.
Yes, does also say that.
hp
--
Adrian Klaver
adrian.klaver@xxxxxxxxxxx
