From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
---|---|
To: | Stephan Szabo <sszabo(at)megazone23(dot)bigpanda(dot)com> |
Cc: | pgsql-patches(at)postgreSQL(dot)org |
Subject: | Re: Proposed patch for qual pushdown into UNION/INTERSECT |
Date: | 2002-08-29 15:24:59 |
Message-ID: | 3577.1030634699@sss.pgh.pa.us |
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Lists: | pgsql-patches |
Stephan Szabo <sszabo(at)megazone23(dot)bigpanda(dot)com> writes:
> I do wonder if queries like
> select * from ((select * from bar1 union all select * from bar2
> union all (select * from bar1 except select * from bar2)) intersect select
> * from bar1) as foo where a>4;
> can push the a>4 restriction into the right side of the intersect which it
> doesn't seem to right now,
Not without a lot more work, which I haven't got time for now.
> We could probably do:
> Subquery
> Intersect
> Append
> Subquery (passing down a>4)
> Subquery (passing down a>4)
> <something> (filter a>4)
> Except
> Subquery
> Subquery
> Subquery (passing down a>4)
> and get the same effect,
Yeah, the problem is the planner doesn't currently cope with attaching
quals to intermediate levels of a set-op tree, so there's no way to
do the above.
> but I think
> the mixed case is probably rare enough
> to not worry about for now.
Agreed. This is still a step forward.
regards, tom lane
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