Oracle 10g Time Zone Confusion

Question

SELECT TO_CHAR(SYSDATE, \'YYYY-MM-DD HH24:MI\')
      ,TO_CHAR(CURRENT_DATE, \'YYYY-MM-DD HH24:MI\')
      ,TO_CHAR(SYSTIMESTAMP, \'YYYY-MM-DD HH24:MI TZR\') 
               


        

Answer 1

There are actually 3 timezones here, not 2

• the timezone of the session/client
  • Shown in SESSIONTIMEZONE
  • This is the timezone of CURRENT_DATE, LOCALTIMESTAMP and CURRENT_TIMESTAMP. The difference between those 3 is the return type, they return a DATE, TIMESTAMP, and TIMESTAMP WITH TIME ZONE respectively)
• The database timezone
  • Shown in DBTIMEZONE
  • This is the the timezone used for the internal storage of TIMESTAMP WITH LOCAL TIME ZONE values. Note that values are converted to/from session timezone on insert/select so it actually isn't as important as it seems
  • This is NOT the timezone of SYSDATE/SYSTIMESTAMP
• The database OS timezone
  • In unix, it is based on the TZ variable when Oracle is started
  • This is the timezone of SYSDATE and SYSTIMESTAMP

In your first example, I can see that the session TZ is UTC-6, the database TZ is UTC, and the database OS timezone is UTC-6.

In your second example, I can see that the session TZ is UTC-6, the database TZ is UTC+2, and the database OS timezone is UTC+1.