From fe084039e482673c2d7fbd881f7ce918c2512d50 Mon Sep 17 00:00:00 2001 From: Tom Lane Date: Wed, 20 Nov 2024 12:03:47 -0500 Subject: [PATCH] Avoid assertion failure if a setop leaf query contains setops. Ordinarily transformSetOperationTree will collect all UNION/ INTERSECT/EXCEPT steps into the setOperations tree of the topmost Query, so that leaf queries do not contain any setOperations. However, it cannot thus flatten a subquery that also contains WITH, ORDER BY, FOR UPDATE, or LIMIT. I (tgl) forgot that in commit 07b4c48b6 and wrote an assertion in rule deparsing that a leaf's setOperations would always be empty. If it were nonempty then we would want to parenthesize the subquery to ensure that the output represents the setop nesting correctly (e.g. UNION below INTERSECT had better get parenthesized). So rather than just removing the faulty Assert, let's change it into an additional case to check to decide whether to add parens. We don't expect that the additional case will ever fire, but it's cheap insurance. Man Zeng and Tom Lane Discussion: https://postgr.es/m/tencent_7ABF9B1F23B0C77606FC5FE3@qq.com --- src/backend/utils/adt/ruleutils.c | 12 +++++++++--- 1 file changed, 9 insertions(+), 3 deletions(-) diff --git a/src/backend/utils/adt/ruleutils.c b/src/backend/utils/adt/ruleutils.c index f0b053e2f6..615ed1f410 100644 --- a/src/backend/utils/adt/ruleutils.c +++ b/src/backend/utils/adt/ruleutils.c @@ -6155,13 +6155,19 @@ get_setop_query(Node *setOp, Query *query, deparse_context *context) Query *subquery = rte->subquery; Assert(subquery != NULL); - Assert(subquery->setOperations == NULL); - /* Need parens if WITH, ORDER BY, FOR UPDATE, or LIMIT; see gram.y */ + + /* + * We need parens if WITH, ORDER BY, FOR UPDATE, or LIMIT; see gram.y. + * Also add parens if the leaf query contains its own set operations. + * (That shouldn't happen unless one of the other clauses is also + * present, see transformSetOperationTree; but let's be safe.) + */ need_paren = (subquery->cteList || subquery->sortClause || subquery->rowMarks || subquery->limitOffset || - subquery->limitCount); + subquery->limitCount || + subquery->setOperations); if (need_paren) appendStringInfoChar(buf, '('); get_query_def(subquery, buf, context->namespaces,