Re: Condition pushdown: why (=) is pushed down into join, but BETWEEN or >= is not? - Mailing list pgsql-hackers

Dmitry Astapov <dastapov@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