Date: Thu, 24 Oct 2002 09:39:14 -0700 (PDT)
From: Stephan Szabo <sszabo@megazone23.bigpanda.com>
To: Tomasz Myrta <jasiek@klaster.net>
Cc: <pgsql-sql@postgresql.org>
Subject: Re: sub-select with aggregate
In-Reply-To: <20021024175129.M3214@klaster.net>
Message-ID: <20021024093022.A21018-100000@megazone23.bigpanda.com>
MIME-Version: 1.0
Content-Type: TEXT/PLAIN; charset=US-ASCII

On Thu, 24 Oct 2002, Tomasz Myrta wrote:

> > The system doesn't realize that it can limit the subquery when the only
> > things it has is the join clause and the limiting clause on the other
> > table.  Like Tom's message about the other view, it won't imply that
> > X.foo=12345 from foo=12345 when the exposed foo is B.foo.
>
> Is this what we should expect, or rather a bug?
> The system knows how to join tables, but fails with joining views or
> subselects :-(

It knows how to join them, it doesn't know that it can change the
clauses given to it in order to make it more efficient.

Basically, as I understand it,
 select * from a,b where a.a=b.a and a.a=3;
isn't going to realize that b.a=3 and act as if
you typed that. It may consider an index scan in
a nested loop for a.a=b.a, but that's not quite
the same.