Fix HAVING-to-WHERE pushdown with nondeterministic collations When GROUP BY uses a nondeterministic collation, the planner's optimization of moving HAVING clauses to WHERE can produce incorrect query results. The HAVING clause may apply a stricter collation that distinguishes values the GROUP BY considers equal. Pushing such a clause to WHERE causes it to filter individual rows before grouping, potentially eliminating group members and changing aggregate results.
Fix this by detecting collation conflicts before flatten_group_exprs, while the HAVING clause still contains GROUP Vars (Vars referencing RTE_GROUP). At that point, each GROUP Var directly carries the GROUP BY collation as its varcollid, making it straightforward to compare against the operator's inputcollid. A mismatch where the GROUP BY collation is nondeterministic means the clause is unsafe to push down. RowCompareExpr is treated specially, since it carries per-column inputcollids[] rather than a single inputcollid. The conflicting clause indices are recorded in a Bitmapset and consulted during the existing HAVING-to-WHERE loop, so that only affected clauses are kept in HAVING; other safe clauses in the same query are still pushed. Back-patch to v18 only. The fix relies on the RTE_GROUP mechanism introduced in v18 (commit 247dea89f), which is what lets us identify grouping expressions and their resolved collations via GROUP Vars on pre-flatten havingQual. Pre-v18 branches lack that machinery, so a back-patch there would need a different approach. Given the absence of field reports of this bug on back branches, the risk of carrying a different fix on stable branches is not justified. Author: Richard Guo <[email protected]> Reviewed-by: wenhui qiu <[email protected]> Discussion: https://postgr.es/m/CAMbWs48Dn2wW6XM94GZsoyMiH42=kgmo+wcobpkuwvgynwa...@mail.gmail.com Backpatch-through: 18 Branch ------ REL_18_STABLE Details ------- https://git.postgresql.org/pg/commitdiff/e8fd5e579223f669245a8f7961c71b94afec2307 Modified Files -------------- src/backend/optimizer/plan/planner.c | 188 ++++++++++++++++++++++ src/test/regress/expected/collate.icu.utf8.out | 213 +++++++++++++++++++++++++ src/test/regress/sql/collate.icu.utf8.sql | 66 ++++++++ src/tools/pgindent/typedefs.list | 1 + 4 files changed, 468 insertions(+)
