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

I have developed the attached doc patch to address your very clear
illustration that our documentation is lacking in this area.

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On Tue, Dec  4, 2012 at 08:18:31PM +0100, Francisco Olarte (M) wrote:
> > Wow, that is a weird case.  In the first test, we count the number of
> > days because it is less than a full month.  In the second case, we call
> > it a full month, but then forget how long it is.  Not sure how we could
> > improve this.
>
> I do not think this needs to be improved, the problem is given two
> dates you can substract them in three different ways,
>
> 1.- (year months)+(days)+(hours minutes seconds), which is what age
> does and is documented as such.
>
> folarte=# select age('2013-11-24 16:41:31','2012-10-23 15:56:10');
>              age
> -----------------------------
>  1 year 1 mon 1 day 00:45:21
> (1 row)
>
> Which is apropiate for things like 'I'm xxx old'
>
> 2.- (days)+(hours-minutes-seconds), which is what substractint dates
> do ( or seems to do for me, as I've done:
>
> select timestamp '2013-11-23 16:41:31' - '2012-10-23 15:56:10';
>      ?column?
> -------------------
>  396 days 00:45:21
>
> Which I can not find a use for, but there sure are and I'm doomed to
> find one soon.
>
> 3.- Exact duration ( I do this a lot at work as I need to calculate
> call durations ):
>
> folarte=# select extract(epoch from timestamp '2013-11-23 16:41:31') -
> extract(epoch from timestamp '2012-10-23 15:56:10');
>  ?column?
> ----------
>  34217121
> (1 row)
>
> folarte=# select (extract(epoch from timestamp '2013-11-23 16:41:31')
> - extract(epoch from timestamp '2012-10-23 15:56:10')) * interval '1
> second';
>   ?column?
> ------------
>  9504:45:21
> (1 row)
>
> The problem I see is intervals are really complicated and difficult to
> undestand, so it is at most a documentation problem ( people usually
> understimate the difficulty of working with them, I see this a lot at
> work ).
>
> Francisco Olarte.

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  Bruce Momjian  <bruce@momjian.us>        http://momjian.us
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