From: | "Francisco Olarte (M)" <folarte(at)peoplecall(dot)com> |
---|---|
To: | Bruce Momjian <bruce(at)momjian(dot)us> |
Cc: | Alvaro Herrera <alvherre(at)2ndquadrant(dot)com>, aanisimov(at)inbox(dot)ru, pgsql-bugs(at)postgresql(dot)org |
Subject: | Re: BUG #7722: extract(epoch from age(...)) appears to be broken |
Date: | 2012-12-04 19:18:31 |
Message-ID: | CA+bJJbzvxnv2_mP4e6nH8Tx3mRuv_u0z7X3NQk+Sm+gLhUTZZA@mail.gmail.com |
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Lists: | pgsql-bugs pgsql-docs |
> 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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