Further fixes for degenerate outer join clauses

Enterprise / PostgreSQL - Tom Lane [sss.pgh.pa.us] - 6 August 2015 14:35 UTC

Further testing revealed that commit f69b4b9495269cc4 was still a few bricks shy of a load: minor tweaking of the previous test cases resulted in the same wrong-outer-join-order problem coming back. After study I concluded that my previous changes in make_outerjoininfo() were just accidentally masking the problem, and should be reverted in favor of forcing syntactic join order whenever an upper outer join's predicate doesn't mention a lower outer join's LHS. This still allows the chained-outer-joins style that is the normally optimizable case.

I also tightened things up some more in join_is_legal(). It seems to me on review that what's really happening in the exception case where we ignore a mismatched special join is that we're allowing the proposed join to associate into the RHS of the outer join we're comparing it to. As such, we should *always* insist that the proposed join be a left join, which eliminates a bunch of rather dubious argumentation. The case where we weren't enforcing that was the one that was already known buggy anyway (it had a violatable Assert before the aforesaid commit) so it hardly deserves a lot of deference.

Back-patch to all active branches, like the previous patch. The added regression test case failed in all branches back to 9.1, and I think it's only an unrelated change in costing calculations that kept 9.0 from choosing a broken plan.

8703059 Further fixes for degenerate outer join clauses.
src/backend/optimizer/README | 23 +++++++---
src/backend/optimizer/path/joinrels.c | 73 ++++++++++++--------------------
src/backend/optimizer/plan/initsplan.c | 28 ++++++------
src/test/regress/expected/join.out | 72 ++++++++++++++++++++++++++++++-
src/test/regress/sql/join.sql | 25 +++++++++++
5 files changed, 153 insertions(+), 68 deletions(-)

Upstream: git.postgresql.org

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