Converting unix timestamp to date after Daylight Saving Time change

Question

Hello,
in one of the products we use the internal scheduler stores dates (and times) in an Unix-like format, that is seconds since 1st of January 1970. We have used this SQL to extract the actual date:
TO_CHAR(t.next_fire_time/(24*60*60*1000) +to_date('19700101020000','yyyymmddhh24miss'),'yyyymmddhh24miss')
Everything worked fine until the time has changed this weekend from UTC+2 to UTC+1 (we are located in Eastern Europe). Since then the query above returns one hour later than it should.
I.e. timestamp *1320067800000* is returned as *20111031153000* even thought correct is (and the actual time the event was scheduled) *31-OCT-11 02.30.16.000000 PM*
I found queries like this on different forums and no one seems to worry much about the daylight savings. Is this a configuration issue in the DB or is it a bug in our code?
I tried selecting the SESSIONTIMEZONE and DBTIMEZONE and both were +1.
Any help appreciated.

Answer 1

Your problem is hard-coded 2hour offset:
to_date('19700101<font size=5 color=red>02</font>0000','yyyymmddhh24miss')You need to calculate current offset to adjust it to current DST situation:
with sample_table as (
                      select date '1970-01-01' + 1320067800000 / 1000 / 3600 / 24 dt_utc from dual
select  dt_utc,
        dt_utc +
        extract(
                     timezone_hour
                from
                     from_tz(cast(dt_utc as timestamp),'utc') at time zone 'Europe/Prague'
               ) / 24 dt_prague,
        extract(
                     timezone_hour
                from
                     from_tz(cast(dt_utc as timestamp),'utc') at time zone 'Europe/Prague'
               ) tz_offset
  from  sample_table
DT_UTC              DT_PRAGUE            TZ_OFFSET
2011-10-31 13:30:00 2011-10-31 14:30:00          1
SQL> SY.