postgresql: timezone sensitive query on a timestamp without timezone - postgresql

Question

I have a table with a timestamp without time zone column (data entered is assumed to be in Australia/Sydney time zone).
Query on data for a time range (ie 8am-4pm) in America/New_York time zone.
Is there an easy way to achieve this?
thanks, p.

Answer 1

Figured it out.
You need to first convert the time to it's with time zone version ie my_ts at time zone 'Australia/Sydney' and then convert that to it's NY counterpart via at time zone 'America/New_York'
select
my_ts as "Default(syd)",
my_ts at time zone 'Australia/Sydney' as "SYD",
my_ts at time zone 'Australia/Sydney' at time zone 'America/New_York' as "NY",
date_part('hour', my_ts at time zone 'Australia/Sydney' at time zone 'America/New_York') as "NY-hr"
from my_table
where date_part('hour', my_ts at time zone 'Australia/Sydney' at time zone 'America/New_York')>=8
and date_part('hour', my_ts at time zone 'Australia/Sydney' at time zone 'America/New_York')<16

Answer 2

You can convert everything to the same time zone so you can compare them with (if the timezone was set):
select current_time, current_time at time zone 'gmt';
timetz | timezone
-------------------+-------------------
20:50:51.07742-07 | 03:50:51.07742+00
If the time zone is not set and you need to correct it some local time:
select now()::time, now()::time + '+8:00'::interval;
now | ?column?
-----------------+-----------------
20:57:49.420742 | 04:57:49.420742
Once you get the time the way you want, just the extract the hour and you can use a simple condition to select the proper times.
select *
from
(select extract(hour from now()::time + '+8:00'::interval) as hour) as t
where hour between 8 and 16;