Re: [SQL] Query based on date/time field

I just wanted to answer the initial question, but Heruoth managed to do so
before me:-) Anyway, I decided to play with datetime and timespan types
and was stuck with strange problem. Here it is:
If I subtract one datetime from another  everithing is going as expected:
userbase=> select '12 Jun 98'::datetime-'11 Jun 98'::datetime;
?column?
--------
@ 1 day
(1 row)

But, subtracting one date from another one I got something like int:
userbase=> select '12 Jun 98'::date-'11 Jun 98'::date;
?column?
--------
       1
(1 row)

The next query explains more clearly that type of result is "int4":
userbase=> select ('12 Jun 98'::date-'11 Jun 98'::date)::datetime;
ERROR:  function datetime(int4) does not exist

Is that what is expected to be or a bug??
( I'm running PostgreSQL 6.3.2p1-4 on Linux (SlackWare) 2.0.34 )

On Wed, 12 Aug 1998, Herouth Maoz wrote:

> At 15:50 +0300 on 12/8/98, Holger Mitterwald wrote:
>
>
> > On Tue, 4 Aug 1998, William McCracken wrote:
> >
> > > I am new to SQL and was wondering how I would go
> > > about selecting records from my database based on
> > > the age of a date/time stamp.
> > >
> > > For example if I wanted to select records older than
> > > 12 hours or 1 day.
> > >
> > > Any help would be appreciated.
> >
> > Sorry for my late response, but I was on holiday.
> > I use some statement like this to select entries that are not older than 2
> > weeks:
> >
> > SELECT DISTINCT landkreis FROM kneipe WHERE 1209600 >= (date_part('epoch',
> > current_date) - date_part('epoch',datum));
> >
> > datum is of type datetime.
> >
> > what I do is the following: epoch returns the seconds since january 1st
> > 1970 (I think). I substract the timestamp of each record from the current
> > timestamp (current_date). The result has to be smaller than the duration
> > for 2 weeks (in seconds, which is 1209600s).
> >
> > I dont know if there is a better solution, but it works fine.
>
> I think the following is simpler and more intuitive:
>
> SELECT * FROM the_table
> WHERE the_date >= ('now'::datetime - '12 hours'::timespan);
>
> This assumes that the field "the_date" in "the_table" is of type datetime.
> If it isn't, just convert it by using datetime( the_date ).
>
> The amount of time described by the type timespan is very intuitive - it
> accepts, as you see, things like '12 hours', '1 day', or '2 months'. It
> takes months correctly - with longer and shorter months taken into
> accounts. More about it in the pgbuiltin manpage.
>
> Herouth
>
> --
> Herouth Maoz, Internet developer.
> Open University of Israel - Telem project
> http://telem.openu.ac.il/~herutma
>
>
>