On Friday, May 22, 2020, Richard Guo <guofengli...@gmail.com> wrote: > Hi hackers, > > For EXISTS SubLink, in some cases the subquery can be reduced to > constant TRUE or FALSE, based on the knowledge that it's being used in > EXISTS(). One such case is when the subquery has aggregates without > GROUP BY or HAVING, and we know its result is exactly one row, unless > that row is discarded by LIMIT/OFFSET. (Greenplum does this.) > > Is it worthwhile to add some codes for such optimization? If so, I can > try to propose a patch >
While the examples clearly demonstrate what you are saying they don’t provide any motivation to do anything about it - adding aggregates and offset to an exists subquery seems like poor query design that should be fixed by the query writer not by spending hacker cycles optimizing it. David J.
