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select to_char(
sys_extract_utc(
to_timestamp_tz('2018-06-08T23:00:00' || '+05:30',
'YYYY-MM-DD"T"HH24:MI:SS TZH:TZM')
), 'YYYY-MM-DD HH24:MI:SS.FF6') as str_utc
from dual;
| STR_UTC |
|---|
| 2018-06-08 17:30:00.000000 |