Re: Converting epoch to timestamp

Michael Glaesemann <grzm(at)myrealbox(dot)com> writes:
> create or replace function epoch_to_timestamp(
> integer
> ) returns timestamp(0)
> language sql as '
> SELECT ''epoch''::timestamp + $1 * ''1 second''::interval;
> ';

This is in fact wrong, unless you live in the British Isles: the
result will be off by your timezone displacement from UTC. Correct
is to use timestamptz not timestamp.

As an example: timestamp 1089953023 equates to Fri Jul 16 2004, 00:43:43 EDT
according to strftime() on my machine (I live in US Eastern zone which
is presently GMT-4). I get

regression=# select 'epoch'::timestamp + 1089953023 * '1 second'::interval;
?column?
---------------------
2004-07-16 04:43:43
(1 row)

regression=# select 'epoch'::timestamptz + 1089953023 * '1 second'::interval;
?column?
------------------------
2004-07-16 00:43:43-04
(1 row)

The first is not right, the second is ...

> I'm wondering if this wouldn't be better as cast rather than explicit
> functions.

A cast from integer is probably a bad idea, seeing that it will break in
2038. You could make an argument for a cast from double though. The
issue to my mind is whether this might be too Unix-centric.

regards, tom lane