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When a subquery references an output of another subquery that gets pulled up, and that output must be wrapped in a PlaceHolderVar because of an intermediate outer join, the PHV expression is pushed down into the subquery. That copy is not preprocessed along with the outer query's expressions, so the two copies can diverge. This used to be harmless, but since commit2ebf25e7djoin removal edits the whole query tree, walking into subqueries, and can trip an assert in ChangeVarNodes if it removes a rel whose Var survives only in such a copy. To fix, preprocess these copies at their owning query level, early in subquery_planner, before anything can consume them (in particular before SubLinks are turned into SubPlans). This covers copies pushed into both LATERAL subquery RTEs and SubLink subselects, and handles nested copies innermost-first. extract_lateral_references no longer preprocesses the copies it pulls out. Correspondingly, the subquery's own processing must leave the contents of an upper-level PHV alone, since the owning level has already preprocessed them: eval_const_expressions returns such a PHV unchanged, and flatten_join_alias_vars no longer recurses into it. Back-patch to v16, as with commit2ebf25e7d. Reported-by: Tender Wang <tndrwang@gmail.com> Author: Richard Guo <guofenglinux@gmail.com> Reviewed-by: Tom Lane <tgl@sss.pgh.pa.us> Discussion: https://postgr.es/m/CAHewXN=kWGAXV537mKtSyBYobGdHhYJVDJJMXXZEmmPWE_zaPw@mail.gmail.com Backpatch-through: 16