| From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
|---|---|
| To: | Martijn van Oosterhout <kleptog(at)svana(dot)org> |
| Cc: | Curt Sampson <cjs(at)cynic(dot)net>, pgsql-general(at)postgresql(dot)org |
| Subject: | Re: View vs. Statement Query Plan |
| Date: | 2002-06-04 23:15:59 |
| Message-ID: | 19935.1023232559@sss.pgh.pa.us |
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| Lists: | pgsql-general |
Martijn van Oosterhout <kleptog(at)svana(dot)org> writes:
> On Tue, Jun 04, 2002 at 01:15:38AM -0400, Tom Lane wrote:
>> I don't doubt that this transformation is valid in some cases ... but
>> I do doubt that it is valid in all cases. If someone can supply a
>> rigorous proof about when it is valid, I'd be willing to look into
>> doing the necessary programming.
> IIRC, union does an implicit DISTINCT (there's UNION ALL, right). So if what
> is being selected is anything other than a simple statement, it'll be very
> hard to prove equivalence (i guess this is what the iscachable is
> for).
Yeah, the UNION vs. UNION ALL difference is one of the things that would
need to be thought about. I think it's more likely that the
transformation would work for UNION ALL than for UNION ... but I have
not had the time to try to work it out.
regards, tom lane
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