From 77c7a17a6e5fefcd55edb6b47fc462a059b983dc Mon Sep 17 00:00:00 2001 From: Richard Guo Date: Wed, 25 Feb 2026 11:13:21 +0900 Subject: [PATCH] Fix unsafe RTE_GROUP removal in simplify_EXISTS_query When simplify_EXISTS_query removes the GROUP BY clauses from an EXISTS subquery, it previously deleted the RTE_GROUP RTE directly from the subquery's range table. This approach is dangerous because deleting an RTE from the middle of the rtable list shifts the index of any subsequent RTE, which can silently corrupt any Var nodes in the query tree that reference those later relations. (Currently, this direct removal has not caused problems because the RTE_GROUP RTE happens to always be the last entry in the rtable list. However, relying on that is extremely fragile and seems like trouble waiting to happen.) Instead of deleting the RTE_GROUP RTE, this patch converts it in-place to be RTE_RESULT type and clears its groupexprs list. This preserves the length and indexing of the rtable list, ensuring all Var references remain intact. Reported-by: Tom Lane Author: Richard Guo Reviewed-by: Tom Lane Discussion: https://postgr.es/m/3472344.1771858107@sss.pgh.pa.us Backpatch-through: 18 --- src/backend/optimizer/plan/subselect.c | 34 +++++++++++++------------- 1 file changed, 17 insertions(+), 17 deletions(-) diff --git a/src/backend/optimizer/plan/subselect.c b/src/backend/optimizer/plan/subselect.c index e9dc9d31f05..e6bc7023562 100644 --- a/src/backend/optimizer/plan/subselect.c +++ b/src/backend/optimizer/plan/subselect.c @@ -1650,8 +1650,6 @@ convert_EXISTS_sublink_to_join(PlannerInfo *root, SubLink *sublink, static bool simplify_EXISTS_query(PlannerInfo *root, Query *query) { - ListCell *lc; - /* * We don't try to simplify at all if the query uses set operations, * aggregates, grouping sets, SRFs, modifying CTEs, HAVING, OFFSET, or FOR @@ -1721,25 +1719,27 @@ simplify_EXISTS_query(PlannerInfo *root, Query *query) query->hasDistinctOn = false; /* - * Since we have thrown away the GROUP BY clauses, we'd better remove the - * RTE_GROUP RTE and clear the hasGroupRTE flag. + * Since we have thrown away the GROUP BY clauses, we'd better get rid of + * the RTE_GROUP RTE and clear the hasGroupRTE flag. To safely get rid of + * the RTE_GROUP RTE without shifting the index of any subsequent RTE in + * the rtable, we convert the RTE to be RTE_RESULT type in-place, and zero + * out RTE_GROUP-specific fields. */ - foreach(lc, query->rtable) + if (query->hasGroupRTE) { - RangeTblEntry *rte = lfirst_node(RangeTblEntry, lc); - - /* - * Remove the RTE_GROUP RTE and clear the hasGroupRTE flag. (Since - * we'll exit the foreach loop immediately, we don't bother with - * foreach_delete_current.) - */ - if (rte->rtekind == RTE_GROUP) + foreach_node(RangeTblEntry, rte, query->rtable) { - Assert(query->hasGroupRTE); - query->rtable = list_delete_cell(query->rtable, lc); - query->hasGroupRTE = false; - break; + if (rte->rtekind == RTE_GROUP) + { + rte->rtekind = RTE_RESULT; + rte->groupexprs = NIL; + + /* A query should only have one RTE_GROUP, so we can stop. */ + break; + } } + + query->hasGroupRTE = false; } return true;