Hi all,
I'm basically looking for a one-liner to convert a timestamptz (or a timestamp
w/o time zone if that turns out to be more convenient) to a string format equal
to what MS uses for their datetimeoffset type. I got almost there with
to_char(ts, 'YYYY-MM-DD HH24:MI:SS.US0 TZH:TZM'). Unfortunately(?), the server
lives at time zone UTC, while we need to convert to both UTC and
Europe/Amsterdam zones. The above always gives me +00 for the TZH output, while
it should be +01 now and +02 in the summer...
I'm dealing with a data virtualisation system (TIBCO TDV) here that connects
different types of data-sources, among which is an MS SQL database with said
type. The virtualisation software uses PostgreSQL (14.10 on Ubuntu Linux 22.04)
for caching data. TDV doesn't understand this datetimeoffset type and treats it
internally as a VARCHAR(34) - hence the string output - which is obviously kind
of hard to work with for aggregations and such.
However, in TDV we can create a translation between TDV functions that accept a
timestamp type and a time zone name with a translation to native PostgreSQL
functions, operands and whatnot. That's what I'm looking for.
It currently have this:
ToDatetimeOffsetNL(~any) : ciscache.ToDatetimeOffsetNL($1)
ToDatetimeOffset(~any,~any) : ciscache.ToDatetimeOffset($1, $2)
In the above, I worked around the issue using a couple of user-defined
functions in PG. That should give a reasonable idea of the desired
functionality, but it's not an ideal solution to my problem:
1). The first function has as a drawback that it changes the time zone for the
entire transaction (not sufficiently isolated to my tastes), while
2). The second function has the benefit that it doesn't leak the time zone
change, but has as drawback that the time zone is now hardcoded into the
function definition, while
3). Both functions need to be created in the caching database before we can use
them, while we have several environments where they would apply (DEV, pre-PROD,
PROD).
/* Based this one on a stackoverflow post */
create or replace function ciscache.ToDatetimeOffset(ts_ timestamptz, tz_ text)
returns varchar(34)
language plpgsql
as $$
begin
perform set_config('timezone', tz_, true /* local */);
return to_char(ts_, 'YYYY-MM-DD HH24:MI:SS.US0 TZH:TZM');
end;
$$;
create or replace function ciscache.ToDatetimeOffsetNL(ts_ timestamptz)
returns varchar(34)
language plpgsql
set timezone to 'Europe/Amsterdam'
as $$
begin
return to_char(ts_, 'YYYY-MM-DD HH24:MI:SS.US0 TZH:TZM');
end;
$$;
Is there a way to do this without functions, or if not, at least without having
to hard-code the time zone or leaking the time zone change to other calls
within the same transaction?
Any suggestions much appreciated.
Groet,
Alban Hertroijs
Data engineer ∙ NieuweStroom
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