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In commit b514a7460d9127ddda6598307272c701cbb133b7, I changed the planner so that it would allow nestloop paths to remain partially parameterized, ie the inner relation might need parameters from both the current outer relation and some upper-level outer relation. That's fine so long as we're talking about distinct parameters; but the patch also allowed creation of nestloop paths for cases where the inner relation's parameter was a PlaceHolderVar whose eval_at set included the current outer relation and some upper-level one. That does *not* work. In principle we could allow such a PlaceHolderVar to be evaluated at the lower join node using values passed down from the upper relation along with values from the join's own outer relation. However, nodeNestloop.c only supports simple Vars not arbitrary expressions as nestloop parameters. createplan.c is also a few bricks shy of being able to handle such cases; it misplaces the PlaceHolderVar parameters in the plan tree, which is why the visible symptoms of this bug are "plan should not reference subplan's variable" and "failed to assign all NestLoopParams to plan nodes" planner errors. Adding the necessary complexity to make this work doesn't seem like it would be repaid in significantly better plans, because in cases where such a PHV exists, there is probably a corresponding join order constraint that would allow a good plan to be found without using the star-schema exception. Furthermore, adding complexity to nodeNestloop.c would create a run-time penalty even for plans where this whole consideration is irrelevant. So let's just reject such paths instead. Per fuzz testing by Andreas Seltenreich; the added regression test is based on his example query. Back-patch to 9.2, like the previous patch.
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