Add 8AM UTC to a date in oracle - sql

Question

I have a date something like below :
Thu Nov 29 18:00:00 CST 2018
Thu Apr 26 01:00:00 BST 2018
I need to convert it to 8AM UTC in oracle.
How do i do this ?
It is a string not date.
Referred link deals with proper dates and there is no accepted answer for it.
Thanks in Advance

Answer 1

Since it's a string you could use regexp_replace.
regexp_replace(nmuloc, '[[:digit:]]{2}:[[:digit:]]{2}:[[:digit:]]{2} [A-Z]{3}', '08:00:00 GMT')

Answer 2

Oracle Setup
CREATE TABLE table_name ( datetime TIMESTAMP WITH TIME ZONE );
INSERT INTO table_name
SELECT TIMESTAMP '2018-11-29 18:00:00 CST' FROM DUAL UNION ALL
SELECT TIMESTAMP '2018-04-26 01:00:00 Europe/London' FROM DUAL UNION ALL
SELECT TIMESTAMP '2018-06-26 00:00:00 Europe/London' FROM DUAL;
Query 1:
Use datetime AS TIME ZONE 'UTC' to convert it from your time zone to UTC
Then use TRUNC() to truncate it back to the start of the UTC day (and also cast it to a date)
Because its now a date, use CAST( ... AS TIMESTAMP ) to get it back to a timestamp
Then use FROM_TZ( ..., 'UTC' ) to get it to be a timestamp in the UTC time zone
Then add INTERVAL '8' HOUR to be 8am.
Like this:
SELECT FROM_TZ(
CAST(
TRUNC( datetime AT TIME ZONE 'UTC' )
AS TIMESTAMP
),
'UTC'
) + INTERVAL '8' HOUR AS utc_date_at_8am_utc
FROM table_name;
Output:
UTC_DATE_AT_8AM_UTC
--------------------------------
30-NOV-18 08.00.00.000000 AM UTC
26-APR-18 08.00.00.000000 AM UTC
25-JUN-18 08.00.00.000000 AM UTC
Note: this translates 2018-06-26 00:00:00 BST to 2018-06-25 23:00:00 UTC before truncating. So it will be the same UTC day (but not necessarily the same day in the local time zone).
Query 2
If this is an issue then just remove the initial time zone conversion:
SELECT FROM_TZ(
CAST(
TRUNC( datetime )
AS TIMESTAMP
),
'UTC'
) + INTERVAL '8' HOUR AS date_at_8am_utc
FROM table_name
Output:
DATE_AT_8AM_UTC
--------------------------------
29-NOV-18 08.00.00.000000 AM UTC
26-APR-18 08.00.00.000000 AM UTC
26-JUN-18 08.00.00.000000 AM UTC