如何使用特定区域的值更新TIMESTAMP WITH TIME ZONE列？

Question

I have a TIMESTAMP WITH TIME ZONE column in my table. I want to update all values with systimestamp at their respective timezones.

I have tried many ways, but i could not dynamically get timezone information from the value and update the same in a single query.

I will provide the necessary structure here.

create table TIMEZONE_TEST
( COLUMN_ONE timestamp with time zone
);

insert into TIMEZONE_TEST values (systimestamp at time zone 'US/Pacific');
insert into TIMEZONE_TEST values (systimestamp at time zone 'Asia/Tokyo');
insert into TIMEZONE_TEST values (systimestamp at time zone 'Asia/Kuala_Lumpur');
insert into TIMEZONE_TEST values (systimestamp at time zone 'Asia/Singapore');
commit;

I need to update all values with systimestamp of particular timezones.

something like

update TIMEZONE_TEST
set COLUMN_ONE = systimestamp at time zone '<TIMEZONE_NAME of the value>';

Thanks for the kind help in advance.

Answer 1

I am not sure whether I got your question properly but I assume it should be this one:

UPDATE TIMEZONE_TEST SET 
COLUMN_ONE = FROM_TZ(CAST(SYSTIMESTAMP AS TIMESTAMP), EXTRACT(TIMEZONE_REGION FROM COLUMN_ONE));

Answer 2

The required answer was

UPDATE TIMEZONE_TEST
SET COLUMN_ONE = SYSTIMESTAMP at time zone EXTRACT(TIMEZONE_REGION FROM COLUMN_ONE);

I modified the answer given by @Wernfried.