Query to convert system date to specific date a time zone

 SELECT
    TO_CHAR( (from_tz(to_timestamp(TO_CHAR(SYSDATE,'DD-MON-YYYY HH24:MI:SS'),'DD-MON-YYYY HH24:MI:SS'),'CST') AT TIME ZONE 'Asia/Calcutta'),'DD-MON-YYYY HH24:MI:SS') DATE_TIME
FROM
    dual