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operating on data from multiple rows?

From: Joshua Daniel Franklin <joshua(at)iocc(dot)com>
To: pgsql-novice(at)postgresql(dot)org
Subject: operating on data from multiple rows?
Date: 2002-10-22 19:06:43
Message-ID: (view raw, whole thread or download thread mbox)
Lists: pgsql-novice
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?

Joshua Daniel Franklin
Network Administrator


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Subject: Re: operating on data from multiple rows?
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