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Oracle SQL: Convert a time from one timezone to another.

If it is 11:49 AM in Zurich/Switzerland on August 22nd, what time is it in Denver?

What if the date is October 30th?

Using a combination of from_tz, to_char and at time zone allows to convert time stamps from one time zone to another:

select
    to_char(from_tz(timestamp '2023-08-22 11:49:00', 'Europe/Zurich') at time zone 'America/Denver', 'hh24:mi') t1,
    to_char(from_tz(timestamp '2023-10-30 11:49:00', 'Europe/Zurich') at time zone 'America/Denver', 'hh24:mi') t2
from
   dual;
--
-- T1      T2   
-- -----   -----
-- 03:49   04:49

The result of t1 is different from t2 because on October 30th, there is no daylight saving time in effect anymore in Zurich, while Denver still enjoys it.

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