postgres_timezones.sql

create table timetest(a timestamp, b timestamp);
insert into timetest values(TIMESTAMP WITH TIME ZONE '2017-03-01 01:00:00+00', TIMESTAMP WITH TIME ZONE '2017-03-01 03:00:00+02');
select * from timetest where a = b;
          a          |          b          
---------------------+---------------------
 2017-03-01 03:00:00 | 2017-03-01 03:00:00
(1 row)
select extract(timezone from a), a, extract(timezone from b), b from timetest where a = b;
ERROR:  timestamp units "timezone" not supported
drop table timetest;
DROP TABLE
create table timetest(a timestamptz, b timestamptz);
insert into timetest values(TIMESTAMP WITH TIME ZONE '2017-03-01 01:00:00+00', TIMESTAMP WITH TIME ZONE '2017-03-01 03:00:00+02');
select extract(timezone_hour from a) tz_a, a, extract(timezone_hour from b) tz_b, b from timetest where a = b;
 tz_a |           a            | tz_b |           b            
------+------------------------+------+------------------------
    2 | 2017-03-01 03:00:00+02 |    2 | 2017-03-01 03:00:00+02
set timezone=utc;
SET
select extract(timezone_hour from a) tz_a, a, extract(timezone_hour from b) tz_b, b from timetest where a = b;
 tz_a |           a            | tz_b |           b            
------+------------------------+------+------------------------
    0 | 2017-03-01 01:00:00+00 |    0 | 2017-03-01 01:00:00+00