Convert timestamp datatype into unix timestamp Oracle

I realize an answer has already been accepted, but I think it should be made clear that the function in that answer doesn't consider the passed in date's time zone offset. A proper Unix timestamp should be calculated at GMT (+0). Oracle's to_date function assumes the passed in date is in the local time zone unless otherwise specified. This problem is exacerbated by the fact that Daylight Saving Time is a real thing. I over came this problem with the following function:

create or replace
  function unix_time_from_date
      (
        in_date   in date,
        in_src_tz in varchar2 default 'America/New_York'
      )
    return integer
  as
    ut      integer       := 0;
    tz      varchar2(8)   := '';
    tz_date timestamp with time zone;
    tz_stmt varchar2(255);
  begin
    /**
     * This function is used to convert an Oracle DATE (local timezone) to a Unix timestamp (UTC).
     *
     * @author James Sumners
     * @date 01 February 2012
     *
     * @param in_date An Oracle DATE to convert. It is assumed that this date will be in the local timezone.
     * @param in_src_tz Indicates the time zone of the in_date parameter.
     *
     * @return integer
     */

    -- Get the current timezone abbreviation (stupid DST)
    tz_stmt := 'select systimestamp at time zone ''' || in_src_tz || ''' from dual';
    execute immediate tz_stmt into tz_date;
    select
      extract(timezone_abbr from tz_date)
    into tz
    from dual;

    -- Get the Unix timestamp
    select
      (new_time(in_date, tz, 'GMT') - to_date('01-JAN-1970', 'DD-MM-YYYY')) * (86400)
    into ut
    from dual;

    return ut;
end unix_time_from_date;

I have some companion functions, unix_time and unix_time_to_date, available at http://jrfom.com/2012/02/10/oracle-and-unix-timestamps-revisited/. I can't believe Oracle has made it all the way to 11g without implementing these.

for date:

   FUNCTION date_to_unix (p_date  date,in_src_tz in varchar2 default 'Europe/Kiev') return number is
begin
    return  round((cast((FROM_TZ(CAST(p_date as timestamp), in_src_tz) at time zone 'GMT') as date)-TO_DATE('01.01.1970','dd.mm.yyyy'))*(24*60*60));
end;

for timestamp:

FUNCTION timestamp_to_unix (p_time  timestamp,in_src_tz in varchar2 default 'Europe/Kiev') return number is
    begin
        return  round((cast((FROM_TZ(p_time, in_src_tz) at time zone 'GMT') as date)-TO_DATE('01.01.1970','dd.mm.yyyy'))*(24*60*60));
    end;

I'm using following method, which differs a little from other answers in that it uses sessiontimezone() function to properly get date

    select
    ( 
      cast((FROM_TZ(CAST(in_date as timestamp), sessiontimezone) at time zone 'GMT') as date) -- in_date cast do GMT
      - 
      TO_DATE('01.01.1970','dd.mm.yyyy') -- minus unix start date
    )
    * 86400000 -- times miliseconds in day
    from dual;

This was what I came up with:

select    substr(extract(day from (n.origstamp - timestamp '1970-01-01 00:00:00')) * 24 * 60 * 60 + 
          extract(hour from (n.origstamp - timestamp '1970-01-01 00:00:00')) * 60 * 60 + 
          extract(minute from (n.origstamp - timestamp '1970-01-01 00:00:00')) * 60 + 
          trunc(extract(second from (n.origstamp - timestamp '1970-01-01 00:00:00')),0),0,15) TimeStamp 
          from tablename;

FWIW

SELECT (SYSDATE - TO_DATE('01-01-1970 00:00:00', 'DD-MM-YYYY HH24:MI:SS')) * 24 * 60 * 60 * 1000 FROM DUAL

For conversion between Oracle time and Unix times I use these functions. They consider your current timezone. You should also add DETERMINISTIC keyword, for example if you like to use such function in a function-based index. Conversion between DATE and TIMESTAMP should be done implicitly by Oracle.

FUNCTION Timestamp2UnixTime(theTimestamp IN TIMESTAMP, timezone IN VARCHAR2 DEFAULT SESSIONTIMEZONE) RETURN NUMBER DETERMINISTIC IS
    timestampUTC TIMESTAMP;
    theInterval INTERVAL DAY(9) TO SECOND;
    epoche NUMBER;
BEGIN
    timestampUTC := FROM_TZ(theTimestamp, timezone) AT TIME ZONE 'UTC';
    theInterval := TO_DSINTERVAL(timestampUTC - TIMESTAMP '1970-01-01 00:00:00');
    epoche := EXTRACT(DAY FROM theInterval)*24*60*60 
        + EXTRACT(HOUR FROM theInterval)*60*60 
        + EXTRACT(MINUTE FROM theInterval)*60 
        + EXTRACT(SECOND FROM theInterval);
    RETURN ROUND(epoche);
END Timestamp2UnixTime;



FUNCTION UnixTime2Timestamp(UnixTime IN NUMBER) RETURN TIMESTAMP DETERMINISTIC IS
BEGIN
    RETURN (TIMESTAMP '1970-01-01 00:00:00 UTC' + UnixTime * INTERVAL '1' SECOND) AT LOCAL;
END UnixTime2Timestamp;

I agree to what Wernfried Domscheit and James Sumners explained in their posts as solutions - mainly because of the timezone and summertime/wintertime issue !

One of the functions I prefer shorter and without dynamic SQL:

-- as Date 
CAST ( FROM_TZ( TIMESTAMP '1970-01-01 00:00:00' + NUMTODSINTERVAL(input_date , 'SECOND') , 'GMT' ) AT TIME ZONE 'Europe/Berlin' AS DATE )

or

-- as Timestamp
FROM_TZ( to_timestamp(Date '1970-01-01' + input_date / 86400 ), 'GMT' ) AT TIME ZONE 'Europe/Berlin'

As "Time Zone" one needs to put the static string (ie 'Europe/Berlin') and not the dbtimezone or sessiontimezone variable, because this might yield a wrong offset because the execution time can be in Summer while the unix Timestamp could be in winter.

All the above do this:-

ORA-01873: the leading precision of the interval is too small

if your dates are TIMESTAMP format.

Here's the correct answer (assuming you're smart enough to have set up your server to use UTC.)

select (cast(sys_extract_utc(current_timestamp) as date) - TO_DATE('1970-01-01 00:00:00','YYYY-MM-DD HH24:MI:SS')) * 86400 as gmt_epoch from dual;

SELECT 
to_char(sysdate, 'YYYY/MM/DD HH24:MI:SS') dt,
round((sysdate - to_date('19700101 000000', 'YYYYMMDD HH24MISS'))*86400) as udt 
FROM dual;