The question:
I have a unix timestamp in seconds and want to convert it to a timestamp with timezone in postgres.
My confusion originates from the fact that the following does not add but removes the time zone:
SELECT to_timestamp(1632610656) at time zone 'Europe/Berlin'
=> "2021-09-26 00:57:36"
If I understand it correctly to_timestamp creates a timestamp with time zone and given this the at time zone 'Europe/Berlin would then remove the time zone? (this feels so strange to me?!).
If I now want to get the timestamp with time zone in Europe/Berlin, is it correct that I need to do the following?
1. Option
SELECT to_timestamp(1632610656) at time zone 'UTC' at time zone 'Europe/Berlin'
=> "2021-09-25 20:57:36+00"
and NOT
2. Option
SELECT to_timestamp(1632610656) at time zone 'Europe/Berlin' at time zone 'Europe/Berlin'
=> "2021-09-25 22:57:36+00"
They obviously have different results. The first one is the correct one, right?
The Solutions:
Below are the methods you can try. The first solution is probably the best. Try others if the first one doesn’t work. Senior developers aren’t just copying/pasting – they read the methods carefully & apply them wisely to each case.
Method 1
Different from what your intuition would tell you, a timestamp with time zone does not have a certain time zone associated. Rather, it is an “absolute timestamp”.
If you want a timestamp with time zone to be displayed in a certain time zone, you have to set the timezone parameter in your database session:
SET timezone = 'Europe/Berlin';
SELECT to_timestamp(1632610656);
If you want a timestamp without time zone that shows what a Berlin clock would show at that time, use AT TIME ZONE:
SELECT to_timestamp(1632610656) AT TIME ZONE 'Europe/Berlin';
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