Getting timezone based on the region - sql

Question

I have my timezone in Pacific time.I want to convert it to the local time based on the region .Below is the example
time region
2017-05-23 14:00:00 Central
2017-05-23 14:00:00 Eastern
2017-05-23 14:00:00 Mountain
What i am looking for
time region time_local
2017-05-23 14:00:00 Central 2017-05-23 16:00:00
2017-05-23 14:00:00 Eastern 2017-05-23 17:00:00
2017-05-23 14:05:00 Mountain 2017-05-23 15:05:00

Answer 1

You can join to the timezone system view to adjust the timestamps:
select
time,
region,
time - tz1.utc_offset + tz2.utc_offset
from Example ex
JOIN pg_timezone_names tz1
on tz1.name = 'US/Pacific'
JOIN pg_timezone_names tz2
on tz2.name = 'US/' || ex.region

Answer 2

Assuming your "time" column type is a correct "timestamp with time zone" (also called or "timestamptz" for short):
create table times (time timestamp with time zone not null, region text not null);
set timezone='US/Pacific';
insert into times (time, region) values
('2017-05-23 14:00:00','US/Central'),
('2017-05-23 14:00:00','US/Eastern'),
('2017-05-23 14:00:00','US/Mountain');
select *, time at time zone region as time_local from times;
time | region | time_local
------------------------+-------------+---------------------
2017-05-23 14:00:00-07 | US/Central | 2017-05-23 16:00:00
2017-05-23 14:00:00-07 | US/Eastern | 2017-05-23 17:00:00
2017-05-23 14:00:00-07 | US/Mountain | 2017-05-23 15:00:00
If your time columns is an ordinary timestamp instead then you need to think about changing it before you'll get insane. The timestamp type does not mean timestamp at all - it means what some clock somewhere will show, which means different thing depending on where you are and which date it is and in which country you check and your database client settings and current environment and after which changes to the clock will politicians do in the future. Do not go this path.

Answer 3

You may use such a conversion as below :
SET TIMEZONE TO 'US/Central';
SELECT now()::timestamp;
current_time
2018-07-25T14:01:50.608042Z
SET TIMEZONE TO 'US/Eastern';
SELECT now()::timestamp;
current_time
2018-07-25T15:01:50.608042Z
SET TIMEZONE TO 'US/Mountain';
SELECT now()::timestamp;
current_time
2018-07-25T13:01:50.608042Z
SQL Fiddle Demo 1
OR alternatively Use :
SET TIMEZONE TO 'US/Central';
SELECT concat(current_date,' ',localtime) as current_time;
current_time
2018-07-25 14:10:57.962193
SET TIMEZONE TO 'US/Eastern';
SELECT concat(current_date,' ',localtime) as current_time;
current_time
2018-07-25 15:10:57.962193
SET TIMEZONE TO 'US/Mountain';
SELECT concat(current_date,' ',localtime) as current_time;
current_time
2018-07-25 13:10:57.962193
SQL Fiddle Demo 2