Fix sorting a child rel by an expression containing a PlaceHolderVar When building sort keys for a child relation, such as the per-child sort columns of a MergeAppend over partitionwise child joins, prepare_sort_from_pathkeys() may need to compute an EquivalenceClass member from the child's targetlist. find_computable_ec_member() accepts a member if all the Vars and quasi-Vars it contains appear in that targetlist. It ignores child members that don't belong to the given relids, but it can still choose a parent member. Usually that is harmless, since a parent member's Vars never appear in a child's targetlist. PlaceHolderVars are different: equal() ignores their phexpr and phrels, so a parent PlaceHolderVar matches its translated copy in the child's targetlist. As a result, an untranslated parent expression could be added to the child plan's targetlist, leading to "variable not found in subplan target lists" errors from setrefs.c.
To fix, when relids is given, also ignore parent members that don't belong to it. This changes nothing for a non-child relation, because any member computable from its targetlist belongs to it anyway. When relids is NULL, only child members are filtered, as before. Also update the comments for prepare_sort_from_pathkeys() to reflect that 'relids' can identify a non-child relation being sorted, which has long been the case. Back-patch to all supported branches. Author: Richard Guo <[email protected]> Reviewed-by: wenhui qiu <[email protected]> Discussion: https://postgr.es/m/CAMbWs48bLLEGy6YC+n01w6=YR=28cj_kpokcagohqr7jbtl...@mail.gmail.com Backpatch-through: 14 Branch ------ REL_18_STABLE Details ------- https://git.postgresql.org/pg/commitdiff/5fb5bef3e454900c2653b830b042705ee1f9deae Modified Files -------------- src/backend/optimizer/path/equivclass.c | 11 +++++-- src/backend/optimizer/plan/createplan.c | 6 ++-- src/test/regress/expected/partition_join.out | 44 ++++++++++++++++++++++++++++ src/test/regress/sql/partition_join.sql | 11 +++++++ 4 files changed, 67 insertions(+), 5 deletions(-)
