Time zone conversion in SQL query

Question

I am using a query to get some application Received Date from Oracle DB which is stored as GMT. Now I have to convert this to Eastern standard/daylight savings time while retrieving. I am using the below query for this:

   select to_char (new_time(application_recv_date,'gmt','est'), 'MON dd, YYYY') from application

It works fine for Standard time. But for daylight savings time we need to convert it to 'edt' based on timezone info. I am not very sure on how to do this. Please help me out

Answer 1

You can use this query, without having to worry about timezone changes.

select to_char(cast(application_recv_date as timestamp) at time zone 'US/Eastern',
               'MON dd, YYYY'
              )
from application;

Ex:

EDT:

select cast(date'2014-04-08' as timestamp) d1,
       cast(date'2014-04-08' as timestamp) at time zone 'US/Eastern' d2
from dual;

D1                                 D2
---------------------------------- -------------------------------------------
08-APR-14 12.00.00.000000 AM       07-APR-14 08.00.00.000000 PM US/EASTERN

EST:

select cast(date'2014-12-08' as timestamp) d1,
       cast(date'2014-12-08' as timestamp) at time zone 'US/Eastern' d2
from dual;

D1                                 D2
---------------------------------- -------------------------------------------
08-DEC-14 12.00.00.000000 AM       07-DEC-14 07.00.00.000000 PM US/EASTERN

UPDATE:

Thanks to Alex Poole for reminding that, when timezone is not specified, local timezone is used for conversion.

To force the date to be recognized as GMT, use from_tz.

from_tz(cast(date'2014-12-08' as timestamp), 'GMT') at time zone 'US/Eastern'

Answer 2

In Oracle, you can achieve this with below query:

Select current_timestamp, current_timestamp at time zone 'Australia/Sydney' from dual;

Where Australia/Sydney is the name of your timezone in which you want to convert your time.

Answer 3

There already a function exists which converts the time of your needed column from one timezone to another:-

 convert_tz("columname or / the time you want to convert", fromTimeZone, ToTimeZone)

For Example:- I want to convert time of dateTIme column from Indian Time (IST) to Brazil TimeZone as my host database time is by default in india it takes indian time:-

1. Indian Time is GMT+5:30
2. Brazil TIme is GMT-5:30

convert_tz(dl.modified_datetime,'+5:30','-3:00') 'modified_time'

So, In this process you can convert it easily.