10/2/2023 0 Comments Postgres create timestamp![]() ![]() If we consider the minute before, it falls into the -07 timezone.Timestamps are crucial to business analysis for a very simple reason: they tell you when things happen. ![]() The interpretation of postgres is to see it in the -08 timezone. 01:00:00 AT time zone 'US/Pacific' has an ambiguity because it belongs to the hour span which happens first in the -07 timezone, and then a second time in the -08 timezone after the DST switch. That said, the conversion can be done with the AT TIME ZONE construct applied to a timestamp without time zone.Īssuming we run this from the US/Pacific time zone: SET time zone 'US/Pacific' Ĭase z when 'P' then 'US/Pacific' when 'M' then 'US/Mountain' end For instance a session in european time will never read 01:00:00-07 as the value of a timestamp with time zone because no european country is ever at GMT-07. It's certainly worth reading the Date/Time types section of the PostgreSQL manual, as well as paying attention to the "return types" column of the table in the AT TIME ZONE documentation for a better understanding of these problems.įirst, when saying that the result would become for example 01:00:00-07, it should be added that this actually depends on the time zone setting of the SQL client. Unfortunately, there is no way to handle DST change with just your two fields. Results: | DATE/TIME FOR US/PACIFIC | DATE/TIME IN UTC | Here is an example where the initial time zone is kept, so you can see the change between '-08' and '-07': SET time zone 'US/Pacific' If you just wanted it to change between '-08' and '-07' depending on the DST setting at that instant in time, this would have been done for you automatically, but you should have use a TIMESTAMPTZ in the first place, to be precise on which instant in time you were representing. 01:00:00 can represent two distinct instants in time in the US/Pacific time zone, so with just 01:00:00 and "P", you've already lost information that you won't be able to recover. Timestamp: 01:00:00 timezone: "P" would become: The problem here in your first example is that there already is some ambiguity: However, this is only valid when there is no ambiguity in the relative value. In principle, if you are in the same relative time zone as the one where you stored the timestamp, you should get the same value back, so if you've set your client in the US/Pacific time zone and if you've stored 03:00:00 in your P time zone, you should get 03:00:00 back. Presumably, you used your "timezone" column ( P or M) with your TIMESTAMP WITHOUT TIME ZONE to compensate for the ambiguity in the input value. A TIMESTAMP WITHOUT TIME ZONE will always be the same value relative to the time zone configured by the client, even if the time zone where you query it from differs: the instant represented by 03:00:00 will be ambiguous and depend on the client settings.When queried, a TIMESTAMPTZ will be adjusted to represent the same instant in time as initially stored (in whichever part of the world this was) as the instant it would be in the current time zone as configured by the client.In PostgreSQL, neither types store the time zone of the value when it was stored, but TIMESTAMPTZ stores the value as a precise instant in time based on the UTC reference, whereas TIMESTAMP WITHOUT TIME ZONE is always relative. (In fact, the specifications seem to be sufficiently confusing so that various RDBMS implement it in a different way.) The difference between TIMESTAMP WITHOUT TIME ZONE and TIMESTAMP WITH TIME ZONE ( TIMESTAMPTZ) can be quite tricky to understand if you consider their names.
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