From: | "Michael Paesold" <mpaesold(at)gmx(dot)at> |
---|---|
To: | "Joshua Daniel Franklin" <joshua(at)iocc(dot)com>, <pgsql-novice(at)postgresql(dot)org> |
Subject: | Re: operating on data from multiple rows? |
Date: | 2002-10-22 19:52:52 |
Message-ID: | 01f701c27a04$9c5db540$4201a8c0@beeblebrox |
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Lists: | pgsql-novice |
Joshua Daniel Franklin <joshua(at)iocc(dot)com> wrote:
> Here is a problem I've run into with an old IMHO poorly designed database:
>
> There is a table ("log") that has fields
>
> username, sessionid, loggedtime, loggeddate, accntstatus
>
> A SELECT might return this data, for example:
>
> bob 1035208 2002-10-11 11:32:00 Start
> bob 1035208 2002-10-11 11:38:00 Stop
> bob 1052072 2002-10-12 10:05:00 Start
> bob 1052072 2002-10-12 10:15:00 Stop
>
> I'm trying to get my head around a SELECT that will return
> only one entry per sessionid with a duration instead of two entries for
> each. If I had two separate tables for Start and Stop it would
> be trivial with a join, but all I can think of is doing a
> "SELECT ... WHERE accntstatus = 'Start'" and then grabbing the
> sessionid and doing a separate SELECT for every record (and then the
> math to get the duration). This seems like a bad idea since thousands
> of records are retrived at a time.
> Am I missing a better way?
A self-join would help...
SELECT start.username, start.sessionid,
((stop.loggeddate + stop.loggedtime)
- (start.loggeddate + start.loggedtime)) as duration
FROM log AS start, log AS stop
WHERE start.accntstatus = 'Start'
AND stop.accntstatus = 'Stop'
AND start.sessionid = stop.sessionid;
(not tested, but try like this)
You probably have to cast the value of the duration.
Best Regards,
Michael Paesold
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