On Wed, Aug 28, 2024 at 7:58 AM David Rowley <dgrowle...@gmail.com> wrote: > On Wed, 28 Aug 2024 at 11:37, Tom Lane <t...@sss.pgh.pa.us> wrote: > > Oh, scratch that, I see you mean this is an additional way to do it > > not the only way to do it. But I'm confused why it works for > > t1.two+1 AS c1 > > but not > > t1.two+t2.two AS c1 > > Those ought to look pretty much the same for this purpose. > > The bms_overlap(pull_varnos(rcon->root, newnode), rcon->relids) test > is false with t1.two+1. Looks like there needs to be a Var from t2 > for the bms_overlap to be true
Exactly. What Tom's patch does is that if the expression contains Vars/PHVs that belong to the subquery, and does not contain any non-strict constructs, then it can escape being wrapped. In expression 't1.two+t2.two', 't2.two' is a Var that belongs to the subquery, and '+' is strict, so it can escape being wrapped. The expression 't1.two+1' does not meet these conditions, so it is wrapped into a PHV, and the PHV contains lateral reference to t1, which results in a nestloop join with a parameterized inner path. That's why Memoize can work in this query. Thanks Richard
