Re: Intersection of two date interval - Mailing list pgsql-sql

Στις Παρασκευή 26 Ιανουάριος 2007 11:50, ο/η A. Kretschmer έγραψε:
> am  Fri, dem 26.01.2007, um 11:39:03 +0200 mailte Suha Onay folgendes:
> > Hi,
> >
> > How can i find the number of days in the intersection of 2 date interval?
> > For example:
> > 1st  interval: (10.01.2007, 20.01.2007)
> > 2nd interval: (13.01.2007, 21.01.2007)
> > The intersection dates are: 13,14,15,16,17,18,19, 20
> > The result is: 8
> >
> > How can i find the result, 8 in an sql query without using CASE
> > statements?
>
> Some time ago i wrote a function for this, i hope it's helpfull for you:
> (not realy tested, be careful!)
>
>
>
> create type start_end as (t1 timestamptz, t2 timestamptz);
>
> create or replace function time_intersect (timestamptz, timestamptz,
> timestamptz, timestamptz) returns start_end as $$ declare
>         _s1     alias for $1;
>         _e1     alias for $2;
>         _s2     alias for $3;
>         _e2     alias for $4;
>         _start  timestamptz;
>         _end    timestamptz;
>         _return start_end;
> begin
>
>         if _s1 < _s2 then
>                 _start := _s2;
>         else
>                 _start := _s1;
>         end if;
>
>         if _e1 < _e2 then
>                 _end := _e1;
>         else
>                 _end := _e2;
>         end if;
>
>         if _start < _end then
>                 _return.t1 := _start;
>                 _return.t2 := _end;
>         else
>                 _return.t1 := NULL;
>                 _return.t2 := NULL;
>         end if;
>
>         return _return;
> end
> $$ language plpgsql;
>
>

Suha,
the function is the number of days in the
maximum of the two start dates , untill , minimum of the two end dates
interval.
But in postgresql (7.4.15 at least) there is no MIN(date,date),MAX(date,date)
functions. So someone has to write them, so you cant avoid some logic there.
Whats your problem with "CASE" statements?
what you are basically looking for is smth like the above implementation
from Andreas.

> test=# set datestyle=german;
> SET
> test=*# select time_intersect('10.01.2007'::date, '20.01.2007'::date,
> '13.01.2007'::date, '21.01.2007'::date); time_intersect
> -------------------------------------------------------
>  ("13.01.2007 00:00:00 CET","20.01.2007 00:00:00 CET")
> (1 row)
>
>
> test=*# select *, t2-t1 from time_intersect('10.01.2007'::date,
> '20.01.2007'::date, '13.01.2007'::date, '21.01.2007'::date); t1
> |           t2            | ?column?
> -------------------------+-------------------------+----------
>  13.01.2007 00:00:00 CET | 20.01.2007 00:00:00 CET | @ 7 days
> (1 row)
>
>
>
>
> Andreas

--
Achilleas Mantzios