On 10/05/2018 18:03, Vlad Khorsun via Firebird-devel wrote: > > To do it, you need to know TZ (or, offset from UTC) used at > America/Sao_Paulo > at given moment, isn't is ? And this offset is also depends on given moment > itself. And in different moments there could be different offsets. > Correct ? >
Yes. > Could you answer my question below ? > > Please, convert to UTC and explain how to do it: > > 2010.03.01 04:00 Europe/Moscow, > 2013.03.01 04:00 Europe/Moscow, > 2016.03.01 04:00 Europe/Moscow > ------------- SQL> select CON> timestamp '2010-03-01 04:00 Europe/Moscow' t1, CON> timestamp '2013-03-01 04:00 Europe/Moscow' t2, CON> timestamp '2016-03-01 04:00 Europe/Moscow' t3 CON> from rdb$database; T1 2010-03-01 04:00:00.0000 Europe/Moscow T2 2013-03-01 04:00:00.0000 Europe/Moscow T3 2016-03-01 04:00:00.0000 Europe/Moscow SQL> select CON> timestamp '2010-03-01 04:00 Europe/Moscow' at time zone 'GMT' x1, CON> timestamp '2013-03-01 04:00 Europe/Moscow' at time zone 'GMT' x2, CON> timestamp '2016-03-01 04:00 Europe/Moscow' at time zone 'GMT' x3 CON> from rdb$database; X1 2010-03-01 01:00:00.0000 GMT X2 2013-03-01 00:00:00.0000 GMT X3 2016-03-01 01:00:00.0000 GMT SQL> select CON> extract(timezone_hour from timestamp '2010-03-01 04:00 Europe/Moscow') tzh1, CON> extract(timezone_hour from timestamp '2013-03-01 04:00 Europe/Moscow') tzh2, CON> extract(timezone_hour from timestamp '2016-03-01 04:00 Europe/Moscow') tzh3 CON> from rdb$database; TZH1 3 TZH2 4 TZH3 3 ------------- Here I show interesting example when DST starts. Two different GMT dates apparently maps to the same America/Sao_Paulo. But if you inspect they timezone displacements, they are different. ------------- SQL> select CON> timestamp '2018-02-18 01:00 GMT' at time zone 'America/Sao_Paulo' t1, CON> timestamp '2018-02-18 02:00 GMT' at time zone 'America/Sao_Paulo' t2 CON> from rdb$database; T1 2018-02-17 23:00:00.0000 America/Sao_Paulo T2 2018-02-17 23:00:00.0000 America/Sao_Paulo SQL> select CON> extract(timezone_hour from timestamp '2018-02-18 01:00 GMT' at time zone 'America/Sao_Paulo') tzh1, CON> extract(timezone_hour from timestamp '2018-02-18 02:00 GMT' at time zone 'America/Sao_Paulo') tzh2 CON> from rdb$database; TZH1 -2 TZH2 -3 ------------- > Regards, > Vlad > > PS It seems i start to understand you - you want to say that rule for > given area (full TZ name ?) describes all possible moments when offset > from UTC is changed. Including DST start\end and changes due to political > reasons. Correct ? > Yes, let's say that rule is defined from UTC to the time zone, and it say, between UTC moment x and y, tz has a displacement of +/- hh:mm. Every range (x-y) must define a displacement. Adriano ------------------------------------------------------------------------------ Check out the vibrant tech community on one of the world's most engaging tech sites, Slashdot.org! http://sdm.link/slashdot Firebird-Devel mailing list, web interface at https://lists.sourceforge.net/lists/listinfo/firebird-devel
