Date: Tue, 12 Dec 2006 19:23:08 -0300
From: Alvaro Herrera <alvherre@commandprompt.com>
To: Marcin =?utf-8?Q?St=C4=99pnicki?= <mstepnicki@gmail.com>
Cc: pgsql-sql@postgresql.org
Subject: Re: Finding gaps in scheduled events
Message-ID: <20061212222308.GP22782@alvh.no-ip.org>
Mail-Followup-To: Marcin =?utf-8?Q?St=C4=99pnicki?= <mstepnicki@gmail.com>,
	pgsql-sql@postgresql.org
References: <pan.2006.12.12.09.08.15.137773@gmail.com>
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Marcin Stępnicki wrote:

> Now I need to create a query to find hours at which each of the type can
> start. So, if it's event A (which take 15 minutes) it can start at:
> 
> 8:00 (to 8:15)
> 8:15 (to 8:30)
> ( 8:30 to 8:45 is already taken )
> 8:45 (to 9:00)
> 9:00 (to 9:15)
> 9:15 (to 9:30)
> ( 9:30 to 10:00 (9:30-9:45 and 9:45-10:00) is already taken))
> 10:00 (to 10:15)

I think something like this should help you:

select my_hour
from test_events right join test_timeline on
((start, finish) overlaps (my_hour, my_hour + 15 * '1 minute'::interval))
where start is null;

With your test data, it shows all the times except for 8:30, 9:30 and
9:45.