From: | Stephan Szabo <sszabo(at)megazone23(dot)bigpanda(dot)com> |
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To: | Tomasz Myrta <jasiek(at)klaster(dot)net> |
Cc: | <pgsql-sql(at)postgresql(dot)org> |
Subject: | Re: sub-select with aggregate |
Date: | 2002-10-24 16:39:14 |
Message-ID: | 20021024093022.A21018-100000@megazone23.bigpanda.com |
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Thread: | |
Lists: | pgsql-sql |
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.
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