Re: BUG #7722: extract(epoch from age(...)) appears to be broken

aanisimov(at)inbox(dot)ru wrote:
> The following bug has been logged on the website:
>
> Bug reference: 7722
> Logged by: Artem Anisimov
> Email address: aanisimov(at)inbox(dot)ru
> PostgreSQL version: 9.2.1
> Operating system: Slackware Linux 14.0/amd64
> Description:
>
> The following to queries give the same result (first arguments to age()
> differ in the day number only, second arguments are identical):
>
> select extract(epoch from age('2012-11-23 16:41:31', '2012-10-23
> 15:56:10'));
>
> and
>
> select extract(epoch from age('2012-11-22 16:41:31', '2012-10-23
> 15:56:10'));

alvherre=# select age('2012-11-22 16:41:31', '2012-10-23 15:56:10');
age
------------------
30 days 00:45:21
(1 fila)

alvherre=# select age('2012-11-23 16:41:31', '2012-10-23 15:56:10');
age
----------------
1 mon 00:45:21
(1 fila)

The problem is that age() returns 30 days in one case, and "one month" in the
other; extract() then considers the month as equivalent to 30 days. This is
documented as such, see [1].

[1] http://www.postgresql.org/docs/current/static/functions-datetime.html

I think if you want a precise computation you should just subtract the two
dates and then extract epoch from the result.

alvherre=# select extract(epoch from timestamp '2012-11-22 16:41:31' - '2012-10-23 15:56:10');
date_part
-----------
2594721
(1 fila)

alvherre=# select extract(epoch from timestamp '2012-11-23 16:41:31' - '2012-10-23 15:56:10');
date_part
-----------
2681121
(1 fila)

--
Álvaro Herrera http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Training & Services