On Fri, May 22, 2020 at 10:59 PM David G. Johnston < david.g.johns...@gmail.com> wrote:
> 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. > Thanks David. I have the same concern that this case is not common enough to worth hacker cycles. Thanks Richard
