timezone aware date_trunc function

Question

The following query

SELECT the_date FROM date_trunc(\'day\', timestamp with time zone 
       \'2001-01-1 00:00:00+0100\') as the_date

resu

Answer 1

@Adam's answer is definitely more helpful. Although I think we can improve on it again because if we're truncating a Timestamp to a single day (or week/month/etc), then we want to make sure that we're dealing with a Date object, not a Timestamp. Otherwise we may give other pieces of code the impression that something just actually happened to occur at midnight (or potentially some other misleading time of day).

So I would use:

SELECT date_trunc('day', some_timestamp AT TIME ZONE users_timezone)::date AS the_date;

which casts the result to a Date, rather than Timestamp.

The result will be something like:

  the_date
------------
 2019-09-14

instead of the more misleading result of:

      the_date
---------------------
 2019-09-14 00:00:00