Robert Haas wrote:
On Wed, Jul 28, 2010 at 6:55 AM, Dimitri Fontaine
<dfonta...@hi-media.com> wrote:
Robert Haas <robertmh...@gmail.com> writes:
But here you want to have different paths for
the same relation that generate *different output*, and the planner
doesn't understand that concept.
Sorry? I though what Equivalence Class provides is the "proving" that
using this qualification or another will *not* affect the output.
In a query like...
SELECT d1.ID, d2.ID
FROM DocPrimary d1
JOIN DocPrimary d2 ON d2.BasedOn=d1.ID
WHERE (d1.ID=234409763) or (d2.ID=234409763)
...you're going to scan d1, scan d2, and then join the results. The
scan of d1 is going to produce different results depending on whether
you evaluate or not d1.ID=234409763, and the scan of d2 is going to
produce different results depending on whether or not you evaluate
d2.BasedOn=234409763.
Wouldn't it be relatively easy, to rewrite the filter expression by
adding expressions, instead of replacing constants, in the disjunctive
case, so the example at hand would become:
WHERE (d1.ID=234409763) or (d2.ID=234409763)
AND (d2.BasedOnID=234409763) or (d2.ID=234409763)
regards,
Yeb Havinga
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