Regarding TZ conversion

Hi ,

What is the right approach for using AT TIME ZONE function?

Option 1: <some_date with tz> AT TIME ZONE 'IST'
Option 2: <some_date with tz> AT TIME ZONE 'Asia/Kolkata'

In the first option, I get +2:00:00 offset (when *timezone_abbrevations =
'Default'*) and for option 2 , +5:30 offset.

I can see multiple entries for IST in pg_timezone_names with
different utc_offset, but in pg_timezone_abbrev there is one entry. I guess
AT TIME ZONE function using the offset shown in pg_timezone_abbrev.

ovdb=> select * from pg_timezone_names where abbrev = 'IST';
name | abbrev | utc_offset | is_dst
---------------------+--------+------------+--------
Asia/Calcutta | IST | 05:30:00 | f
Asia/Kolkata | IST | 05:30:00 | f
Europe/Dublin | IST | 01:00:00 | t
posix/Asia/Calcutta | IST | 05:30:00 | f
posix/Asia/Kolkata | IST | 05:30:00 | f
posix/Europe/Dublin | IST | 01:00:00 | t
posix/Eire | IST | 01:00:00 | t
Eire | IST | 01:00:00 | t

ovdb=> select * from pg_timezone_abbrevs where abbrev = 'IST';
abbrev | utc_offset | is_dst
--------+------------+--------
IST | 02:00:00 | f

In my system, we receive TZ in abbrev format (3 character, like EST, PST
...).

I have tried changing the timezone_abbrevations = 'India', then it worked
fine (IST is giving +5:30 offset)

So,
What is recommended, use name instead of abbrev in TZ conversion
function?
Or
Change the timezone_abbrevations to 'India'?

*Regards,*
*Rajin *