I shoved some preliminary refactoring into the 0001 patch, notably splitting deconstruct_jointree into two passes. 0002-0009 cover the same ground as they did before, though with some differences in detail. 0010-0012 are new work mostly aimed at removing kluges we no longer need.
I'm looking at 0010-0012 and I really like the changes and removals there. Thanks for the great work!
For 0010, the change seems quite independent. I think maybe we can apply it to HEAD directly.
For 0011, I found that some clauses that were outerjoin_delayed and thus not equivalent before might be treated as being equivalent now. For example
explain (costs off) select * from a left join b on a.i = b.i where coalesce(b.j, 0) = 0 and coalesce(b.j, 0) = a.j; QUERY PLAN ---------------------------------- Hash Right Join Hash Cond: (b.i = a.i) Filter: (COALESCE(b.j, 0) = 0) -> Seq Scan on b -> Hash -> Seq Scan on a Filter: (j = 0) (7 rows)
This is different behavior from HEAD. But I think it's an improvement.
For 0012, I'm still trying to understand JoinDomain. AFAIU all EC members of the same EC should have the same JoinDomain, because for constants we match EC members only within the same JoinDomain, and for Vars if they come from different join domains they will have different nullingrels and thus will not match. So I wonder if we can have the JoinDomain kept in EquivalenceClass rather than in each EquivalenceMembers.
