Although I'm all for following the standard, I wonder of making this
change is the right one to do.
The current behaviour makes a lot of sense to me, and I'm not sure if
the behaviour defined by the standard will make things understandable
for users.
Mark
On 05-04-2020 02:07, Adriano dos Santos Fernandes (JIRA) wrote:
Conversion from WITH TIME ZONE to WITHOUT TIME ZONE types should drop the time
zone instead of use the session time zone
------------------------------------------------------------------------------------------------------------------------
Key: CORE-6276
URL: http://tracker.firebirdsql.org/browse/CORE-6276
Project: Firebird Core
Issue Type: Bug
Components: Engine
Affects Versions: 4.0 Beta 1
Reporter: Adriano dos Santos Fernandes
Firebird (as well PostgreSQL) uses the session time zone when converting from
WITH-TZ to WITHOUT-TZ types.
Example:
set time zone '-03:00';
SQL> select cast(timestamp '2020-04-04 10:00:00 -05:00' as timestamp) from
rdb$database;
CAST
=========================
2020-04-04 12:00:00.0000
When converting it back to TIMESTAMP WITH-TZ (not altering the session time
zone), we get an equal (equivalent) timestamp (which different offset):
SQL> select cast(timestamp '2020-04-04 12:00:00.0000' as timestamp with time
zone) from rdb$database;
CAST
=========================================================
2020-04-04 12:00:00.0000 -03:00
SQL> select timestamp '2020-04-04 12:00:00.0000 -03:00' = timestamp '2020-04-04
10:00:00 -05:00' from rdb$database;
=======
<true>
However the standard SQL says that conversion from TIMESTAMP WITH-TZ to TIMESTAMP
WITHOUT-TZ should be "SV.UTC + SV.TZ" (SV is the source value). In practice
this means to drop the time zone.
Oracle implementation also respects (and documents in
https://docs.oracle.com/cd/B19306_01/server.102/b14225/ch4datetime.htm) this behavior:
"Insert the same date and time as a TIMESTAMP WITH TIME ZONE literal. Oracle
converts it to a TIMESTAMP value, which means that the time zone information is
dropped.".
Also accordingly to the standard the conversion from WITHOUT-TZ to WITH-TZ is "TV.UTC = SV
- STZD; TV.TZ = STZD" (TV is target value; STZD is the session time zone). So in this
respect we are correct and then converting WITH-TZ -> WITHOUT-TZ -> WITH-TZ does not
necessarily produces an equivalent value.
--
Mark Rotteveel
Firebird-Devel mailing list, web interface at
https://lists.sourceforge.net/lists/listinfo/firebird-devel
