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Our support for multiple-set-clauses in UPDATE assumes that the Params referencing a MULTIEXPR_SUBLINK SubPlan will appear before that SubPlan in the targetlist of the plan node that calculates the updated row. (Yeah, it's a hack...) In some PG branches it's possible that a Result node gets inserted between the primary calculation of the update tlist and the ModifyTable node. setrefs.c did the wrong thing in this case and left the upper-level Params as Params, causing a crash at runtime. What it should do is replace them with "outer" Vars referencing the child plan node's output. That's a result of careless ordering of operations in fix_upper_expr_mutator, so we can fix it just by reordering the code. Fix fix_join_expr_mutator similarly for consistency, even though join nodes could never appear in such a context. (In general, it seems likely to be a bit cheaper to use Vars than Params in such situations anyway, so this patch might offer a tiny performance improvement.) The hazard extends back to 9.5 where the MULTIEXPR_SUBLINK stuff was introduced, so back-patch that far. However, this may be a live bug only in 9.6.x and 10.x, as the other branches don't seem to want to calculate the final tlist below the Result node. (That plan shape change between branches might be a mini-bug in itself, but I'm not really interested in digging into the reasons for that right now. Still, add a regression test memorializing what we expect there, so we'll notice if it changes again.) Per bug report from Eduards Bezverhijs. Discussion: https://postgr.es/m/b6cd572a-3e44-8785-75e9-c512a5a17a73@tieto.com |
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