Re: Technique for turning time ranges into a graph

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
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Andreas Kretschmer
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