Getting timezone in oracle

SELECT DISTINCT tzname, TZ_OFFSET (tzname)
FROM V$TIMEZONE_NAMES
ORDER BY tzname;

ALTER SESSION SET time_zone = '-04:00';

SELECT TO_CHAR (CURRENT_TIMESTAMP, 'dd-mon-yyyy HH:mi:ss PM') c_time
FROM DUAL; 

Previous Data Query in Oracle

Data of Five minutes past:

select * from employees as of timestamp(sysdate-interval '5' minute)

insert into emplyess
select * from employees as of timestamp(sysdate-interval '5' minute)

 

 

select * from AC_VOUCHERDTL as of timestamp sysdate-interval '30' minute
minus
select * from AC_VOUCHERDTL