Date: Thu, 21 Jun 2007 07:58:00 +0200
From: "A. Kretschmer" <andreas.kretschmer@schollglas.com>
To: pgsql-sql@postgresql.org
Subject: Re: Technique for turning time ranges into a graph
Message-ID: <20070621055800.GA1405@a-kretschmer.de>
References: <467A06BC.6090900@obviously.com>
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am  Wed, dem 20.06.2007, um 22:03:56 -0700 mailte Bryce Nesbitt folgendes:
> I have a bunch of data which is expressed in terms of start and stop dates,
> e.g.:
> 
> +----------------------------------------------------------------+
> | Member         | Start                 | Stop                  |
> |----------------+-----------------------+-----------------------|
> | Fred           | 2007-01-01            | 2007-05-01            |
> |----------------+-----------------------+-----------------------|
> | Joe            | 2005-05-04            | 2007-04-01            |
> |----------------+-----------------------+-----------------------|
> | Freddie        | 2002-02-01            | 2006-04-01            |
> |----------------+-----------------------+-----------------------|
> | ...            | ...                   | ...                   |
> +----------------------------------------------------------------+
> 
> And what I want is a graph over time showing the number of members on each day.
> 
> Thus the input is rows with time ranges, and the output is a scalar for each
> time bucket.  The time bucket might be months, days, hours, or quarter hours.
> Such a data series could then be loaded into a spreadsheet or otherwise
> graphed.
> 
> I've got a perl script that can do this.  But is there a good and fast way to
> do this in the database?  If I had views with the scalar data, then I could do

Yes, play with generate_series like this:

test=*# select * from member;
  name   |   start    |    stop
---------+------------+------------
 Fred    | 2007-01-01 | 2007-05-01
 Joe     | 2005-05-04 | 2007-04-01
 Freddie | 0202-02-01 | 2006-04-01
(3 rows)

test=*# select foo.date, count(1) from member, (select
('2005-01-01'::date + (generate_series(0,20)||'month')::interval)::date)
foo  where foo.date between start and stop group by 1 order by 1;
    date    | count
------------+-------
 2005-01-01 |     1
 2005-02-01 |     1
 2005-03-01 |     1
 2005-04-01 |     1
 2005-05-01 |     1
 2005-06-01 |     2
 2005-07-01 |     2
 2005-08-01 |     2
 2005-09-01 |     2
 2005-10-01 |     2
 2005-11-01 |     2
 2005-12-01 |     2
 2006-01-01 |     2
 2006-02-01 |     2
 2006-03-01 |     2
 2006-04-01 |     2
 2006-05-01 |     1
 2006-06-01 |     1
 2006-07-01 |     1
 2006-08-01 |     1
 2006-09-01 |     1
(21 rows)


Andreas
-- 
Andreas Kretschmer
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