From c59dd93bc3510c9c20ddc4097ba42de20c113000 Mon Sep 17 00:00:00 2001 From: Andrey Rachitskiy Date: Fri, 21 Aug 2026 09:53:58 +0500 Subject: [PATCH] Fix semijoin RHS unique-ification to use join collation When unique-ifying a semijoin RHS for JOIN_UNIQUE_*, pathkeys and Unique take collation from the RHS expression (SortGroupClause does not carry one). That can be a different (deterministic) collation than the join's inputcollid. Unique then leaves values that are still equal under the join, and the subsequent INNER join duplicates outer rows. Force each semi_rhs_expr to expose the join operator's input collation via canonicalize_ec_expression (RelabelType). BUG #19633 Author: Andrey Rachitskiy Reported-by: Suyang Zhong Discussion: https://www.postgresql.org/message-id/19633-647cd4c73a84b085@postgresql.org --- src/backend/optimizer/plan/initsplan.c | 12 +++++++- .../regress/expected/collate.icu.utf8.out | 29 +++++++++++++++++++ src/test/regress/sql/collate.icu.utf8.sql | 13 +++++++++ 3 files changed, 53 insertions(+), 1 deletion(-) diff --git a/src/backend/optimizer/plan/initsplan.c b/src/backend/optimizer/plan/initsplan.c index f08a918146c..20834d7fcc7 100644 --- a/src/backend/optimizer/plan/initsplan.c +++ b/src/backend/optimizer/plan/initsplan.c @@ -2628,7 +2628,17 @@ compute_semijoin_info(PlannerInfo *root, SpecialJoinInfo *sjinfo, List *clause) /* so far so good, keep building lists */ semi_operators = lappend_oid(semi_operators, opno); - semi_rhs_exprs = lappend(semi_rhs_exprs, copyObject(right_expr)); + + /* + * Ensure that the RHS expression exposes the join operator's input + * collation. The expression will later be used as a grouping key when + * unique-ifying the RHS, so its collation must agree with the semijoin + * equality semantics. + */ + semi_rhs_exprs = lappend(semi_rhs_exprs, + canonicalize_ec_expression((Expr *) copyObject(right_expr), + exprType(right_expr), + op->inputcollid)); } /* Punt if we didn't find at least one column to unique-ify */ diff --git a/src/test/regress/expected/collate.icu.utf8.out b/src/test/regress/expected/collate.icu.utf8.out index fcfcc658bea..a7ca794a0a2 100644 --- a/src/test/regress/expected/collate.icu.utf8.out +++ b/src/test/regress/expected/collate.icu.utf8.out @@ -1988,6 +1988,35 @@ ORDER BY 1; ghi (4 rows) +-- Unique-ification of an IN/semijoin RHS must use the join collation. +CREATE TABLE t_semi_ci (c1 text COLLATE case_insensitive); +CREATE TABLE t_semi_cs (c0 text); +INSERT INTO t_semi_ci VALUES ('a'), ('x'), ('y'); +INSERT INTO t_semi_cs VALUES ('a'), ('a'); +ANALYZE t_semi_ci, t_semi_cs; +INSERT INTO t_semi_cs VALUES ('A'); +SELECT count(*) FROM t_semi_ci WHERE c1 IN (SELECT c0 FROM t_semi_cs); + count +------- + 1 +(1 row) + +SET enable_hashagg TO off; +EXPLAIN (COSTS OFF) +SELECT count(*) FROM t_semi_ci WHERE c1 IN (SELECT c0 FROM t_semi_cs); + QUERY PLAN +--------------------------------------------------------------------- + Aggregate + -> Nested Loop + Join Filter: (t_semi_ci.c1 = ((t_semi_cs.c0)::text)) + -> Unique + -> Sort + Sort Key: t_semi_cs.c0 COLLATE case_insensitive + -> Seq Scan on t_semi_cs + -> Seq Scan on t_semi_ci +(8 rows) + +RESET enable_hashagg; CREATE TABLE test1ci (x text COLLATE case_insensitive); CREATE TABLE test2ci (x text COLLATE case_insensitive); CREATE TABLE test3ci (x text COLLATE case_insensitive); diff --git a/src/test/regress/sql/collate.icu.utf8.sql b/src/test/regress/sql/collate.icu.utf8.sql index ce4e2bb3ffd..b4994c64262 100644 --- a/src/test/regress/sql/collate.icu.utf8.sql +++ b/src/test/regress/sql/collate.icu.utf8.sql @@ -721,6 +721,19 @@ SELECT * FROM test3cs t1 WHERE t1.x = t2.x COLLATE case_insensitive) ORDER BY 1; +-- Unique-ification of an IN/semijoin RHS must use the join collation. +CREATE TABLE t_semi_ci (c1 text COLLATE case_insensitive); +CREATE TABLE t_semi_cs (c0 text); +INSERT INTO t_semi_ci VALUES ('a'), ('x'), ('y'); +INSERT INTO t_semi_cs VALUES ('a'), ('a'); +ANALYZE t_semi_ci, t_semi_cs; +INSERT INTO t_semi_cs VALUES ('A'); +SELECT count(*) FROM t_semi_ci WHERE c1 IN (SELECT c0 FROM t_semi_cs); +SET enable_hashagg TO off; +EXPLAIN (COSTS OFF) +SELECT count(*) FROM t_semi_ci WHERE c1 IN (SELECT c0 FROM t_semi_cs); +RESET enable_hashagg; + CREATE TABLE test1ci (x text COLLATE case_insensitive); CREATE TABLE test2ci (x text COLLATE case_insensitive); CREATE TABLE test3ci (x text COLLATE case_insensitive); -- 2.53.0