Re: Good candidate query for window syntax?

On Sep 10, 9:08 am, jgo...@gmail.com (Jorge Godoy) wrote:
> Have you checked the OVERLAPS operator in the documentation?
>
> http://www.postgresql.org/docs/8.4/interactive/functions-datetime.html
>
> --

> Jorge Godoy     <jgo...@gmail.com>

>
>
>
> On Fri, Sep 10, 2010 at 10:03, Ketema Harris <ket...@gmail.com> wrote:
> > Hello,  I have a table defined as:
>
> > CREATE TABLE demo AS
> > (
> >        id serial PRIMARY KEY,
> >        start_time timestamp without timezone,
> >        duration integer
> > )
>
> > A sample data set I am working with is:
>
> >      start_time      | duration |       end_time
> > ---------------------+----------+---------------------
> >  2006-08-28 16:55:11 |       94 | 2006-08-28 16:56:45
> >  2006-08-28 16:56:00 |       63 | 2006-08-28 16:57:03
> >  2006-08-28 16:56:02 |       25 | 2006-08-28 16:56:27
> >  2006-08-28 16:56:20 |       11 | 2006-08-28 16:56:31
> >  2006-08-28 16:56:20 |       76 | 2006-08-28 16:57:36
> >  2006-08-28 16:56:29 |       67 | 2006-08-28 16:57:36
> >  2006-08-28 16:56:45 |       21 | 2006-08-28 16:57:06
> >  2006-08-28 16:56:50 |       44 | 2006-08-28 16:57:34
> >  2006-08-28 16:56:50 |       36 | 2006-08-28 16:57:26
> >  2006-08-28 16:56:53 |       26 | 2006-08-28 16:57:19
> >  2006-08-28 16:56:57 |       55 | 2006-08-28 16:57:52
> >  2006-08-28 16:57:28 |        1 | 2006-08-28 16:57:29
> >  2006-08-28 16:57:42 |       17 | 2006-08-28 16:57:59
> >  2006-08-28 16:57:46 |       28 | 2006-08-28 16:58:14
> >  2006-08-28 16:58:25 |       51 | 2006-08-28 16:59:16
> >  2006-08-28 16:58:31 |       20 | 2006-08-28 16:58:51
> >  2006-08-28 16:58:35 |       27 | 2006-08-28 16:59:02
>
> > generated by the query:
> > SELECT start_time, duration, to_timestamp((extract(epoch from start_time) +
> > duration))::timestamp as end_time
> > FROM demo
> > ORDER BY start_time, duration, 3;
>
> > My goal is: To find the maximum number of concurrent rows over an arbitrary
> > interval.  Concurrent is defined as overlapping in their duration.  Example
> > from the set above: Assume the desired interval is one day.  Rows 1 and 2
> > are concurrent because row 2's start_time is within the duration of row 1.
> >  If you go through the set the max concurrency is 5 (this is a guess cause I
> > did it visually and may have miscounted). I took a scan of how I tried to
> > solve it manually and attached the image.  I tried using timelines to
> > visualize the start, duration, and end of each row then looked for where
> > they overlapped.
>
> > My desired output set would be:
>
> > max_concurrency     |     interval   (in this case grouped by day)
> > --------------------+-----------------
> >        5           |   2006-08-28
>
> > if the interval for this set were different, say 30 minutes, then I would
> > expect to see something like:
> > max_concurrency     |     interval
> > --------------------+--------------------------------------------
> >        0           |   2006-08-28 00:00:00 - 2006-08-28 00:29:59
> >        0           |   2006-08-28 00:30:00 - 2006-08-28 00:59:59
> >        0           |   2006-08-28 01:00:00 - 2006-08-28 01:29:59
> >                        .......continues.....
> >        0           |   2006-08-28 16:00:00 - 2006-08-28 16:29:59
> >        5           |   2006-08-28 16:30:00 - 2006-08-28 16:59:59
>
> > I think that a query that involves a window could be used to solve this
> > question as the documentation says:
> > "A window function call represents the application of an aggregate-like
> > function over some portion of the rows selected by a query...the window
> > function is able to scan all the rows that would be part of the current
> > row's group according to the grouping specification...."
> > I am hoping that someone with more experience could help devise a way to do
> > this with a query.  Thanks in advance.
>
> > --

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I have just reviewed and thanks for reminding me that exists.  I can
see that this could be useful, but I'm not quite putting it all
together.  The overlaps operator takes two sets of start and end times
and tells you if they overlap, i need this comparison done over an
entire set......I started writing the following:

SELECT count(case when (start_time, end_time) overlaps ?  is true then
1) as max_concurrency OVER w,
   calldate::date as "interval"
OVER (PARTITION BY start_time::date ORDER BY start_time, end_time
desc) AS w
ROWS BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING
FROM cdr;

What would go on the right side of overlaps ?

I really have no idea if that is the right direction....

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