Reply-To: <jtx@hatesville.com>
From: "James Taylor" <jtx@hatesville.com>
To: <pgsql-sql@postgresql.org>
Subject: Coalesce/Join/Entries may not exist.
Date: Mon, 9 Jun 2003 05:00:16 -0700
Message-ID: <000101c32e7e$b4353a10$0300a8c0@theplague>
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I've got three tables, I'll shorten the columns down just so you get the
idea:

lists
-----------
id|order_id

list_results
------------
id|lid|total

orders
------------
id|max

All of the columns are int's.  What I'm trying to do is something like:

select (o.max-coalesce(sum(lr.total),0)) from orders o,list_results lr
where lr.l_id in (select
   l.id from lists l, orders o where l.order_id=X and o.id=l.order_id)
group by o.max

This would, in theory, return a number which should be
o.total-sum(lr.total)

The problem is, there may not be any data in list_results OR lists
regarding the order ID.  If data from list_results.total exists, and is
referencing lists.id, which in turn is referencing orders.id through
lists.order_id, return o.max-lr.total.  If data from list_results or
lists DOESN'T exist, I would just want to go ahead and return
orders.max.  I was hoping the coalesce would be able to do this, but it
doesn't.  The subquery is in there because frankly I'm not sure how to
do multiple left joins, which I think would have to exist.  The easy way
out for me here I think would be to make list_results.order_id and leave
lists out of it, but then I'd have redundant data in two tables.  Any
suggestions on this one?