Oracle EDT/EST time to GMT conversion - oracle

Question

all dates which we store in oracle are in EDT(summer) and EST(winter). I need a way to convert that date to UTC/GMT.
The conversion should be based on the db date and not the servers local TZ.
In other words if the date in the resultset is between:
"11/02/2014 02:00:00" ---> "03/08/2015 01:59:59": TZ offset = "-0500"
"03/08/2015 02:00:00" ---> "11/01/2015 01:59:59": TZ offset = "-0400".
And same for previous years.
Is there a solution for that?

Answer 1

Assuming some_date_column is actually a date column then you can turn it into a timestamp with time zone using a cast (from date to timestamp) and the from_tz function with a region that has the EST/EDT change defined:
with t (some_date_column) as (
select to_date('11/02/2014 02:00:00', 'MM/DD/YYYY HH24:MI:SS') from dual
union all
select to_date('03/08/2014 01:59:59', 'MM/DD/YYYY HH24:MI:SS') from dual
union all
select to_date('03/08/2015 03:00:00', 'MM/DD/YYYY HH24:MI:SS') from dual
union all
select to_date('11/01/2015 00:59:59', 'MM/DD/YYYY HH24:MI:SS') from dual
union all
select to_date('11/01/2015 01:59:59', 'MM/DD/YYYY HH24:MI:SS') from dual
union all
select to_date('11/02/2015 02:00:00', 'MM/DD/YYYY HH24:MI:SS') from dual
)
select t.some_date_column,
cast(t.some_date_column as timestamp) as some_timestamp,
from_tz(cast(t.some_date_column as timestamp), 'America/New_York')
as some_timestamp_tz
from t;
SOME_DATE_COLUMN SOME_TIMESTAMP SOME_TIMESTAMP_TZ
------------------- ------------------- ---------------------------
11/02/2014 02:00:00 11/02/2014 02:00:00 11/02/2014 02:00:00 -05:00
03/08/2014 01:59:59 03/08/2014 01:59:59 03/08/2014 01:59:59 -05:00
03/08/2015 03:00:00 03/08/2015 03:00:00 03/08/2015 03:00:00 -04:00
11/01/2015 00:59:59 11/01/2015 00:59:59 11/01/2015 00:59:59 -04:00
11/01/2015 01:59:59 11/01/2015 01:59:59 11/01/2015 01:59:59 -05:00
11/02/2015 02:00:00 11/02/2015 02:00:00 11/02/2015 02:00:00 -05:00
This doesn't quite line up with the ranges in your question. There is no 02:00 when you move from EST to EDT, so I've used 03:00 in the demo CTE instead; and as the period between 01:00 and 02:00 is (sort of) repeated when you go the other way from EDT to EST the offset for a plain time in that hour is ambiguous, and Oracle is choosing to treat it as -05:00 rather than -04:00.
If you want the UTC equivalent of the EST/EDT time then you can then use at time zone, and optionally cast back to a date:
...
select t.some_date_column,
from_tz(cast(t.some_date_column as timestamp), 'America/New_York')
at time zone 'UTC' as utc_timestamp_tz,
cast(from_tz(cast(t.some_date_column as timestamp), 'America/New_York')
at time zone 'UTC' as date) as utc_date
from t;
SOME_DATE_COLUMN UTC_TIMESTAMP_TZ UTC_DATE
------------------- --------------------------- -------------------
11/02/2014 02:00:00 11/02/2014 07:00:00 +00:00 11/02/2014 07:00:00
03/08/2014 01:59:59 03/08/2014 06:59:59 +00:00 03/08/2014 06:59:59
03/08/2015 03:00:00 03/08/2015 07:00:00 +00:00 03/08/2015 07:00:00
11/01/2015 00:59:59 11/01/2015 04:59:59 +00:00 11/01/2015 04:59:59
11/01/2015 01:59:59 11/01/2015 06:59:59 +00:00 11/01/2015 06:59:59
11/02/2015 02:00:00 11/02/2015 07:00:00 +00:00 11/02/2015 07:00:00
If your original column is a timestamp (with no time zone information) rather than a date then you can skip the first cast from date to timestamp, but still use from_tz to specify it's original region.