Richard Guo <guofengli...@gmail.com> writes: > On Fri, May 26, 2023 at 6:06 AM Tom Lane <t...@sss.pgh.pa.us> wrote: >> Based on what deconstruct_distribute_oj_quals is doing, it seems >> likely to me that there are cases that require ignoring >> commute_above_r, but I've not tried to devise one. It'd be good to >> have one to include in the commit, if we can find one.
> It seems that queries of the second form of identity 3 require ignoring > commute_above_r. > select 1 from t t1 left join (t t2 left join t t3 on t2.a = t3.a) on > t1.a = t2.a; > When removing t2/t3 join, the clone of 't2.a = t3.a' with t1 join in the > nulling bitmap would be put back if we do not ignore commute_above_r. > There is no observable problem though because it would be rejected later > in subbuild_joinrel_restrictlist, but still I think it should not be put > back in the first place. Ah. I realized that we could make the problem testable by adding assertions that a joinclause we're not removing doesn't contain any surviving references to the target rel or join. That turns out to fire (without the bug fix) in half a dozen existing test cases, so I felt that we didn't need to add another one. I did the other refactoring we discussed and pushed it. Thanks for the report and review! regards, tom lane