Dmitry Astapov <dasta...@gmail.com> writes:
> Am I right in thinking that elimination the join condition is actually
> quite important part of the process?
> Could it possibly be the main reason for =ANY/(x IN (..)) not to be
> optimized the same way?
Yup.
> Is it still hard when one thinks about =ANY or (column in (val1, val2,
> val3, ...)) as well?
Yeah. For instance, if you have
WHERE a = b AND a IN (1,2,3)
then yes, you could deduce "b IN (1,2,3)", but this would not give you
license to drop the "a = b" condition. So now you have to figure out
what the selectivity of that is after the application of the partially
redundant IN clauses.
I recall somebody (David Rowley, maybe? Too lazy to check archives.)
working on this idea awhile ago, but he didn't get to the point of
a committable patch.
regards, tom lane
