Remove useless timzone from function - sql

Question

I have postgresql function that receive date variable, then I trunc day from time, but timezone anyway added to final query.
CREATE OR REPLACE FUNCTION public.request_user_track()
RETURNS trigger
LANGUAGE plpgsql
AS $function$
BEGIN
IF TG_OP = 'INSERT' THEN
PERFORM pg_notify('user_log_added', '{"userID": ' || NEW."userID" || ',"time":"' || NEW.time || '"}');
INSERT INTO "UserTracks"("userID", "day", "requestedAt", "createdAt", "updatedAt")
VALUES(NEW."userID", date_trunc('day', NEW."time" AT TIME ZONE 'UTC'), NOW() + interval '1 second', NOW(), NOW())
ON CONFLICT("userID", "day") DO UPDATE SET "requestedAt" = EXCLUDED."requestedAt"
WHERE "UserTracks"."userID" = NEW."userID" AND "UserTracks".day = date_trunc('day', NEW."time" AT TIME ZONE 'UTC');
END IF;
RETURN NULL;
END;
$function$
;
I try to set timezone, but anyway in final query I have in db: 2019-12-30 03:00:00

Answer 1

Ok, given that the type of day is timestamptz in the db '2019-12-30 03:00:00' stored at MSK (+3) timezone, I believe the database is doing the right thing.
If you think about it, '2019-12-30 03:00:00 +03:00' is the same time as '2019-12-30 00:00:00 +00:00'. Now we just want the same timestamp to be stored at UTC timezone.
I have a hunch, try something like:
INSERT INTO "UserTracks"("userID", "day", ...)
VALUES(NEW."userID", date_trunc('day', NEW."time" AT TIME ZONE 'UTC') AT TIME ZONE 'UTC', ...)
It may be the case the result of date_trune() isn't kept at UTC timezone.
The other thing to note is that if this is deployed to a production server configured to run its OS and PostgreSQL in UTC (generally recommended) these issues won't exist.

Answer 2

You could change your session timezone or simply variable::timestamp or SELECT variable AT TIME ZONE 'desirable_timezone'. If you only want the date, then DATE(variable). It will depend on what you want to achieve, but all methods are valid for querying or modifing your table, with or without date_trunc.
SELECT date_trunc('day',date(now()))