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. > > -- > Sent via pgsql-general mailing list (pgsql-general@postgresql.org) > To make changes to your subscription: > http://www.postgresql.org/mailpref/pgsql-general > >
