From b574fec00f275e50ffe2c9780ec1f6398796c905 Mon Sep 17 00:00:00 2001 From: Tom Lane Date: Sun, 28 Jun 2026 12:31:29 -0400 Subject: [PATCH] Avoid collation lookup failure when considering a "char" column. If a "char" column has a statistics histogram, scalarineqsel() would fail with "cache lookup failed for collation 0". Avoid the failing lookup by acting as though the collation is "C". Prior to commit 06421b084, this code didn't fail because lc_collate_is_c() intentionally didn't spit up on InvalidOid. It did act differently though: it would take the non-C-collation code path and hence apply strxfrm using libc's prevailing locale. But that seems like the wrong thing for a non-collatable comparison, so let's not resurrect that aspect. Author: Feng Wu Reviewed-by: Tom Lane Discussion: https://postgr.es/m/CACK3muq6s-O1Wc3w4dRL1Fe8YQ-Fz1zJbezeQwhuLgNxGNEFiA@mail.gmail.com Backpatch-through: 18 --- src/backend/utils/adt/selfuncs.c | 8 ++++++++ src/test/regress/expected/planner_est.out | 11 +++++++++++ src/test/regress/sql/planner_est.sql | 6 ++++++ 3 files changed, 25 insertions(+) diff --git a/src/backend/utils/adt/selfuncs.c b/src/backend/utils/adt/selfuncs.c index d6efd07073a..cbc70fde716 100644 --- a/src/backend/utils/adt/selfuncs.c +++ b/src/backend/utils/adt/selfuncs.c @@ -5295,6 +5295,14 @@ convert_string_datum(Datum value, Oid typid, Oid collid, bool *failure) return NULL; } + /* + * If we don't have a collation, act as though it's "C". This would + * normally happen only for the "char" type, but perhaps there are other + * cases. + */ + if (!OidIsValid(collid)) + return val; + mylocale = pg_newlocale_from_collation(collid); if (!mylocale->collate_is_c) diff --git a/src/test/regress/expected/planner_est.out b/src/test/regress/expected/planner_est.out index b62a47552fa..236cb274a78 100644 --- a/src/test/regress/expected/planner_est.out +++ b/src/test/regress/expected/planner_est.out @@ -210,4 +210,15 @@ false, true, false, true); -> Result (cost=N..N rows=1 width=N) (4 rows) +-- Verify that scalarineqsel() works on "char" columns +CREATE TEMP TABLE char_table_1 AS + SELECT i::"char" AS c FROM generate_series(64,96) i; +ANALYZE char_table_1; +EXPLAIN (COSTS OFF) SELECT * FROM char_table_1 WHERE c < 'Q'; + QUERY PLAN +----------------------------- + Seq Scan on char_table_1 + Filter: (c < 'Q'::"char") +(2 rows) + DROP FUNCTION explain_mask_costs(text, bool, bool, bool, bool); diff --git a/src/test/regress/sql/planner_est.sql b/src/test/regress/sql/planner_est.sql index 53210d5baad..2b696a4e4e5 100644 --- a/src/test/regress/sql/planner_est.sql +++ b/src/test/regress/sql/planner_est.sql @@ -147,4 +147,10 @@ SELECT explain_mask_costs($$ SELECT * FROM tenk1 WHERE unique1 <> ALL (ARRAY[1, 2, 98, (SELECT 99), NULL]);$$, false, true, false, true); +-- Verify that scalarineqsel() works on "char" columns +CREATE TEMP TABLE char_table_1 AS + SELECT i::"char" AS c FROM generate_series(64,96) i; +ANALYZE char_table_1; +EXPLAIN (COSTS OFF) SELECT * FROM char_table_1 WHERE c < 'Q'; + DROP FUNCTION explain_mask_costs(text, bool, bool, bool, bool);