Changed historic time zones in timezone database

Detail name	Value
Changelog Number	23470
Type	Improvement
Status	Resolved
Fix Versions	Exasol 8.34.0
Resolution Date	2025-04-16

Background

Exasol database use Time Zone Database provided by IANA for handling of datetime-related data types.

Improvement

We updated the timezone database to version 2025a.

Change in behavior with historic time zone conversions

Version 2024b of the time zone database (https://www.iana.org/time-zones) changed the definition of some time zones. This affects some historic time zone conversions.

Example

For example, CET prior to May 1892 had a different offset of 42 minutes and 30 seconds.

-- Old behavior: 1 row, values ('1111-11-11 10:11:11.000000')
-- New behavior: 1 row, values ('1111-11-11 10:53:41.000000')
select convert_tz(timestamp'1111-11-11 11:11:11', 'CET', 'UTC');

Further details

The NEWS changelog for version 2024b of the time zone database explains that it tidies up some time zone names to remove duplicate data. This affects some conversions of time zones EET (before 1981), CET (before 1947), MET and WET (before 1996).

(For example, CET used to be defined in terms of the C-Eur rules but now it is just a link to Europe/Brussels in the “backward” (compatibility) file. C-Eur and Europe/Brussels have different rules prior to 1947.)

The same results as in the example above can be seen in recent versions of other programs such as date and python.

$ TZ=UTC date --date='TZ="CET" 1111-11-11 11:11:11' +"%x %X"
11/11/11 10:53:41

Changed behavior

We updated the time zone database to version 2025a. The new version changed the definition of some time zones. Some historic time zone conversions now give different results, for example CET prior to May 1892.