How to get server OS local time in all Postgres versions - sql

Question

How to get server local time in char(8) format hh:mm:ss in every Postgres version.
In 9.1 it works:
select current_time::char(8)
returns proper local time 13:46:00
In 9.5 it returns 3 hour different time:
10:46:00
select current_time, version() returns
"10:48:40.181735+00";"PostgreSQL 9.5.2, compiled by Visual C++ build 1800, 32-bit"
and
"13:48:51.775138+03";"PostgreSQL 9.1.2 on x86_64-unknown-linux-gnu, compiled by gcc-4.4.real (Debian 4.4.5-8) 4.4.5, 64-bit"
Update
Both servers use default postgres.conf settings for time.
postgres.conf does not contain timezone settings.
in 9.5 Windows 10 it contains
#timezone = 'GMT'
#timezone_abbreviations = 'Default'
in 9.1 Debian it contains
#timezone = '(defaults to server environment setting)'
#timezone_abbreviations = 'Default'
How to get server local time in 9.5 when default postgresql.conf file is used ?
It looks like server does not use OS setting in 9.5
How to force 9.5 to ask timezone from OS and return time in this zone?

Answer 1

Ask for the time zone you want:
select current_time at time zone 'brt';
timezone
--------------------
08:26:16.778448-03
If you need a string:
select to_char(current_timestamp at time zone 'brt', 'HH24:MI:SS');
to_char
----------
08:32:07
Notice that the to_char function does not accept the time type. Use timestamp instead.
Get the OS local time zone from the shell. In Linux:
$ date +%Z
BRT
In psql:
=> \! date +%Z
BRT
If there is psql at the client:
psql -c "\! date +%Z" --host localhost --dbname=cpn --no-password
BRT
It is necessary a .pgpass file to avoid supplying the password.

Answer 2

If timezone is not specified in postgresql.conf or as a server command-line option, the server attempts to use the value of the TZ environment variable as the default time zone. If TZ is not defined or is not any of the time zone names known to PostgreSQL, the server attempts to determine the operating system's default time zone by checking the behavior of the C library function localtime(). The default time zone is selected as the closest match among PostgreSQL's known time zones. (These rules are also used to choose the default value of log_timezone, if not specified.) source
This means that if you do not define a timezone, the server attempts to determine the operating system's default time zone by checking the behavior of the C library function localtime().
If timezone is not specified in postgresql.conf or as a server command-line option, the server attempts to use the value of the TZ environment variable as the default time zone.
I believe you need to remove the # in #timezone = 'GMT'
And replace GMT with '(defaults to server environment setting)'
Because '(defaults to server environment setting)' is undefined and thus the server attempts to determine the operating system's default time zone by checking the behavior of the C library function localtime().

Answer 3

To obtain the local time calculated with the defined timezone:
select current_time, version();
To obtain the local time calculated with a specified timezone:
select current_time at time zone 'US/Eastern';
To obtain the defined timezone:
SELECT current_setting('TIMEZONE');
To assign the timezone that you want to use:
set timezone='US/Eastern';
You can see the different timezones here