MDEV-35845 Let string constants enter multiple equalities for all collations

SELECT * FROM t1 WHERE v IN ('a','b') AND v = 'b' kept both conjuncts when v is a utf8mb4 column, while the same query on a latin1 column was simplified to v = 'b'. BETWEEN and the constant in a join equality (t1.v = t2.v AND t1.v = 'b') were left alone in the same way. The rewrite is done by the multiple equality machinery, not by propagate_cond_constants(). check_simple_equality() turns v = 'b' into an Item_equal holding the column and the constant. Later substitute_for_best_equal_field() walks the remaining predicates, and Item_func_in::propagate_equal_fields() asks each argument that is a column of an Item_equal to replace itself with that constant whenever the predicate compares under the Item_equal's collation. 'b' IN ('a','b') is then constant and remove_eq_conds() folds it away. The same path serves BETWEEN, <=> and every other comparison, and eliminate_item_equal() derives t2.v = 'b' from the join equality. A constant was only admitted into an Item_equal when the column's collation handler reported propagate() true. That flag was added in 2005 for Bug#9509, when a constant taken from an Item_equal was substituted into any expression, so LENGTH(s1) saw 'oe' instead of the o-umlaut it equals under latin1_german2_ci. Every utf8mb3 and utf8mb4 case-insensitive collation and every UCA collation report false, so once MDEV-19123 made utf8mb4 the default, no string column got a constant in its Item_equal. Since MDEV-7152 the substitution is decided per site by a Context: comparison operators accept the constant only when their comparison collation is the Item_equal's, everything else only for binary no-pad collations, and LIKE refuses pad and non-1-to-1 collations on its own. The flag therefore duplicated a finer check, and propagate_cond_constants() had been substituting the same constants into = and < under the same collations without consulting it. Field_str::test_if_equality_guarantees_uniqueness() no longer consults it either; the remaining tests, that the constant compares as a string and under the column's own collation, stay. That exposes one case the flag was hiding. Charset narrowing (cset_narrowing) lets a utf8mb3_general_ci column and a utf8mb4_general_ci column share an Item_equal, so the Item_equal now also has to hold a utf8mb4 constant for its utf8mb3 member. eliminate_item_equal() manufactures utf8mb3_col = utf8mb4_const for that member, which fails collation aggregation when the constant has a character outside the BMP. Field_longstr::get_equal_const_item() converts the constant from the Item_equal's comparison collation into the member's character set, through the mb4-to-mb3 narrowing charset when narrowing applies, so that a character outside the BMP becomes U+FFFD, which is what utf8mb4_general_ci compares it as. It returns NULL, and the equality is dropped, when the constant cannot be represented. eliminate_item_equal() calls it for every member it builds an equality for; Item_field::propagate_equal_fields() already did. The tests added to func_in.test come from Dave Gosselin's patch for this issue, which handled IN in propagate_cond_constants() instead. Two of its expectations change with this approach: an Item_equal prints its constant first, and v IN ('a',NULL) AND v = 'b' now folds to an impossible WHERE, as 'b' IN ('a',NULL) is NULL. The other re-recorded results show the same reordering, or improved plans where a constant now reaches another table. In main.ps and main.join a self-join of INFORMATION_SCHEMA tables on TABLE_NAME now narrows both sides to the named table, so the InnoDB tables in the data directory are no longer opened and their "Unknown storage engine" warnings disappear. In spider/bugfix.mdev_27172 the CASE greeting WHEN 'Aloha!' ... = 'one' conjunct, used there to keep the group by handler out, folds to TRUE once greeting is substituted by its constant, so the condition Spider pushes down to the remote is now just greeting = 'Aloha!'. This commit was prepared with Claude Code (Fable 5.1), which traced the missing rewrite to the propagate() check, showed by experiment that removing it restores the rewrite and passes the func_in tests, found the narrowing failure from a query supplied by the author, wrote Field_longstr::get_equal_const_item() and its call in eliminate_item_equal(), re-recorded the affected results, and ran the main suite in normal and --ps-protocol mode before and after.
2026-10-23 18:49:29 +03:00 · 2026-10-15 10:38:35 +13:00
parent dddbd5ff42
commit 8e11a253d0
22 changed files with 416 additions and 57 deletions
--- a/mysql-test/main/cset_narrowing.result
+++ b/mysql-test/main/cset_narrowing.result
@@ -303,7 +303,7 @@ EXPLAIN
          "rows": 4,
          "cost": "COST_REPLACED",
          "filtered": 100,
-          "index_condition": "t1.mb3 = '????' or t1.mb3 = 'hello'"
+          "index_condition": "t1.mb3 = '<EFBFBD>' or t1.mb3 = 'hello'"
        }
      }
    ]
@@ -520,7 +520,7 @@ EXPLAIN
          "rows": 1,
          "cost": "COST_REPLACED",
          "filtered": 100,
-          "index_condition": "t1.mb3 = t10.mb4"
+          "index_condition": "t1.mb3 = 'hello'"
        }
      },
      {
@@ -536,7 +536,7 @@ EXPLAIN
          "rows": 1,
          "cost": "COST_REPLACED",
          "filtered": 100,
-          "index_condition": "t2.mb4 = t10.mb4 and concat(convert(t1.mb3 using utf8mb4),t2.mb4,t10.mb4) <> 'Bebebe'"
+          "index_condition": "t2.mb4 = 'hello' and concat(convert(t1.mb3 using utf8mb4),t2.mb4,t10.mb4) <> 'Bebebe'"
        }
      }
    ]
@@ -553,15 +553,15 @@ JS
        [
            {
                "transformation": "equality_propagation",
-                "resulting_condition": "t10.mb4 = 'hello' and concat(convert(t1.mb3 using utf8mb4),t2.mb4,t10.mb4) <> 'Bebebe' and multiple equal(t1.mb3, t2.mb4, t10.mb4)"
+                "resulting_condition": "concat(convert(t1.mb3 using utf8mb4),t2.mb4,t10.mb4) <> 'Bebebe' and multiple equal('hello', t1.mb3, t2.mb4, t10.mb4)"
            },
            {
                "transformation": "constant_propagation",
-                "resulting_condition": "t10.mb4 = 'hello' and concat(convert(t1.mb3 using utf8mb4),t2.mb4,t10.mb4) <> 'Bebebe' and multiple equal(t1.mb3, t2.mb4, t10.mb4)"
+                "resulting_condition": "concat(convert(t1.mb3 using utf8mb4),t2.mb4,t10.mb4) <> 'Bebebe' and multiple equal('hello', t1.mb3, t2.mb4, t10.mb4)"
            },
            {
                "transformation": "trivial_condition_removal",
-                "resulting_condition": "t10.mb4 = 'hello' and concat(convert(t1.mb3 using utf8mb4),t2.mb4,t10.mb4) <> 'Bebebe' and multiple equal(t1.mb3, t2.mb4, t10.mb4)"
+                "resulting_condition": "concat(convert(t1.mb3 using utf8mb4),t2.mb4,t10.mb4) <> 'Bebebe' and multiple equal('hello', t1.mb3, t2.mb4, t10.mb4)"
            }
        ]
    }
--- a/mysql-test/main/ctype_cp1250_ch.result
+++ b/mysql-test/main/ctype_cp1250_ch.result
@@ -220,7 +220,7 @@ EXPLAIN EXTENDED SELECT a, LENGTH(a) FROM t1 WHERE a NOT LIKE 'a ' AND a='a';
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
 1	SIMPLE	t1	ALL	NULL	NULL	NULL	NULL	2	100.00	Using where
 Warnings:
-Note	1003	select `test`.`t1`.`a` AS `a`,octet_length(`test`.`t1`.`a`) AS `LENGTH(a)` from `test`.`t1` where `test`.`t1`.`a`  not like 'a ' and `test`.`t1`.`a` = 'a'
+Note	1003	select `test`.`t1`.`a` AS `a`,octet_length(`test`.`t1`.`a`) AS `LENGTH(a)` from `test`.`t1` where `test`.`t1`.`a` = 'a' and `test`.`t1`.`a`  not like 'a '
 DROP TABLE t1;
 #
 # End of MDEV-8694
--- a/mysql-test/main/ctype_uca.result
+++ b/mysql-test/main/ctype_uca.result
@@ -8522,7 +8522,7 @@ EXPLAIN EXTENDED SELECT a, LENGTH(a) FROM t1 WHERE a NOT LIKE 'a ' AND a='a';
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
 1	SIMPLE	t1	ALL	NULL	NULL	NULL	NULL	2	100.00	Using where
 Warnings:
-Note	1003	select `test`.`t1`.`a` AS `a`,octet_length(`test`.`t1`.`a`) AS `LENGTH(a)` from `test`.`t1` where `test`.`t1`.`a`  not like 'a ' and `test`.`t1`.`a` = 'a'
+Note	1003	select `test`.`t1`.`a` AS `a`,octet_length(`test`.`t1`.`a`) AS `LENGTH(a)` from `test`.`t1` where `test`.`t1`.`a` = 'a' and `test`.`t1`.`a`  not like 'a '
 DROP TABLE t1;
 #
 # End of MDEV-8694
@@ -8680,7 +8680,7 @@ EXPLAIN EXTENDED SELECT a, LENGTH(a) FROM t1 WHERE a NOT LIKE 'a ' AND a='a';
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
 1	SIMPLE	t1	ALL	NULL	NULL	NULL	NULL	2	100.00	Using where
 Warnings:
-Note	1003	select `test`.`t1`.`a` AS `a`,octet_length(`test`.`t1`.`a`) AS `LENGTH(a)` from `test`.`t1` where `test`.`t1`.`a`  not like 'a ' and `test`.`t1`.`a` = 'a'
+Note	1003	select `test`.`t1`.`a` AS `a`,octet_length(`test`.`t1`.`a`) AS `LENGTH(a)` from `test`.`t1` where `test`.`t1`.`a` = 'a' and `test`.`t1`.`a`  not like 'a '
 DROP TABLE t1;
 #
 # End of MDEV-8694
--- a/mysql-test/main/ctype_utf8.result
+++ b/mysql-test/main/ctype_utf8.result
@@ -9421,7 +9421,7 @@ EXPLAIN EXTENDED SELECT * FROM t1 WHERE (a,a)=(10,'1e1');
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
 1	SIMPLE	t1	ALL	NULL	NULL	NULL	NULL	2	100.00	Using where
 Warnings:
-Note	1003	select `test`.`t1`.`a` AS `a` from `test`.`t1` where `test`.`t1`.`a` = 10 and `test`.`t1`.`a` = '1e1'
+Note	1003	select `test`.`t1`.`a` AS `a` from `test`.`t1` where `test`.`t1`.`a` = '1e1' and `test`.`t1`.`a` = 10
 DROP TABLE t1;
 #
 # MDEV-8688 Wrong result for SELECT..WHERE varchar_column IN (1,2,3) AND varchar_column=' 1';
--- a/mysql-test/main/ctype_utf8mb3_general_ci.result
+++ b/mysql-test/main/ctype_utf8mb3_general_ci.result
@@ -575,7 +575,7 @@ EXPLAIN EXTENDED SELECT a, LENGTH(a) FROM t1 WHERE a NOT LIKE 'a ' AND a='a';
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
 1	SIMPLE	t1	ALL	NULL	NULL	NULL	NULL	2	100.00	Using where
 Warnings:
-Note	1003	select `test`.`t1`.`a` AS `a`,octet_length(`test`.`t1`.`a`) AS `LENGTH(a)` from `test`.`t1` where `test`.`t1`.`a`  not like 'a ' and `test`.`t1`.`a` = 'a'
+Note	1003	select `test`.`t1`.`a` AS `a`,octet_length(`test`.`t1`.`a`) AS `LENGTH(a)` from `test`.`t1` where `test`.`t1`.`a` = 'a' and `test`.`t1`.`a`  not like 'a '
 DROP TABLE t1;
 #
 # End of MDEV-8694
--- a/mysql-test/main/ctype_utf8mb3_uca1400_ai_ci.result
+++ b/mysql-test/main/ctype_utf8mb3_uca1400_ai_ci.result
@@ -575,7 +575,7 @@ EXPLAIN EXTENDED SELECT a, LENGTH(a) FROM t1 WHERE a NOT LIKE 'a ' AND a='a';
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
 1	SIMPLE	t1	ALL	NULL	NULL	NULL	NULL	2	100.00	Using where
 Warnings:
-Note	1003	select `test`.`t1`.`a` AS `a`,octet_length(`test`.`t1`.`a`) AS `LENGTH(a)` from `test`.`t1` where `test`.`t1`.`a`  not like 'a ' and `test`.`t1`.`a` = 'a'
+Note	1003	select `test`.`t1`.`a` AS `a`,octet_length(`test`.`t1`.`a`) AS `LENGTH(a)` from `test`.`t1` where `test`.`t1`.`a` = 'a' and `test`.`t1`.`a`  not like 'a '
 DROP TABLE t1;
 #
 # End of MDEV-8694
--- a/mysql-test/main/ctype_utf8mb4_general_ci.result
+++ b/mysql-test/main/ctype_utf8mb4_general_ci.result
@@ -575,7 +575,7 @@ EXPLAIN EXTENDED SELECT a, LENGTH(a) FROM t1 WHERE a NOT LIKE 'a ' AND a='a';
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
 1	SIMPLE	t1	ALL	NULL	NULL	NULL	NULL	2	100.00	Using where
 Warnings:
-Note	1003	select `test`.`t1`.`a` AS `a`,octet_length(`test`.`t1`.`a`) AS `LENGTH(a)` from `test`.`t1` where `test`.`t1`.`a`  not like 'a ' and `test`.`t1`.`a` = 'a'
+Note	1003	select `test`.`t1`.`a` AS `a`,octet_length(`test`.`t1`.`a`) AS `LENGTH(a)` from `test`.`t1` where `test`.`t1`.`a` = 'a' and `test`.`t1`.`a`  not like 'a '
 DROP TABLE t1;
 #
 # End of MDEV-8694
--- a/mysql-test/main/ctype_utf8mb4_uca1400_ai_ci.result
+++ b/mysql-test/main/ctype_utf8mb4_uca1400_ai_ci.result
@@ -575,7 +575,7 @@ EXPLAIN EXTENDED SELECT a, LENGTH(a) FROM t1 WHERE a NOT LIKE 'a ' AND a='a';
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
 1	SIMPLE	t1	ALL	NULL	NULL	NULL	NULL	2	100.00	Using where
 Warnings:
-Note	1003	select `test`.`t1`.`a` AS `a`,octet_length(`test`.`t1`.`a`) AS `LENGTH(a)` from `test`.`t1` where `test`.`t1`.`a`  not like 'a ' and `test`.`t1`.`a` = 'a'
+Note	1003	select `test`.`t1`.`a` AS `a`,octet_length(`test`.`t1`.`a`) AS `LENGTH(a)` from `test`.`t1` where `test`.`t1`.`a` = 'a' and `test`.`t1`.`a`  not like 'a '
 DROP TABLE t1;
 #
 # End of MDEV-8694
--- a/mysql-test/main/func_in.result
+++ b/mysql-test/main/func_in.result
@@ -1276,3 +1276,203 @@ drop table t1;
 #
 # End of 10.6 tests
 #
+#
+# MDEV-35845 WHERE COL IN (item0, item1, ..., itemN) AND COL = item1
+# Optimization
+#
+create table t1 (v varchar(64), t text, c char(32));
+insert into t1 values ('a','a','a'),('b','b','b');
+explain extended select * from t1 where v in ('a','b') and v = 'b';
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
+1	SIMPLE	t1	ALL	NULL	NULL	NULL	NULL	2	100.00	Using where
+Warnings:
+Note	1003	select `test`.`t1`.`v` AS `v`,`test`.`t1`.`t` AS `t`,`test`.`t1`.`c` AS `c` from `test`.`t1` where `test`.`t1`.`v` = 'b'
+explain extended select * from t1 where t in ('a','b') and t = 'b';
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
+1	SIMPLE	t1	ALL	NULL	NULL	NULL	NULL	2	100.00	Using where
+Warnings:
+Note	1003	select `test`.`t1`.`v` AS `v`,`test`.`t1`.`t` AS `t`,`test`.`t1`.`c` AS `c` from `test`.`t1` where `test`.`t1`.`t` = 'b'
+explain extended select * from t1 where c in ('a','b') and c = 'b';
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
+1	SIMPLE	t1	ALL	NULL	NULL	NULL	NULL	2	100.00	Using where
+Warnings:
+Note	1003	select `test`.`t1`.`v` AS `v`,`test`.`t1`.`t` AS `t`,`test`.`t1`.`c` AS `c` from `test`.`t1` where `test`.`t1`.`c` = 'b'
+explain extended select * from t1 where v not in ('a','b') and v = 'b';
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
+1	SIMPLE	NULL	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Impossible WHERE
+Warnings:
+Note	1003	select `test`.`t1`.`v` AS `v`,`test`.`t1`.`t` AS `t`,`test`.`t1`.`c` AS `c` from `test`.`t1` where 0
+select * from t1 where v in ('a','b') and v = 'b';
+v	t	c
+b	b	b
+select * from t1 where v in ('a','x') and v = 'b';
+v	t	c
+select * from t1 where v not in ('a','b') and v = 'b';
+v	t	c
+drop table t1;
+# The predicant is left alone when the IN predicate and the equality
+# compare with different collations.  Under utf8mb3_german2_ci the
+# o-umlaut row matches 'oe', under utf8mb3_general_ci it does not, so
+# the two predicates ask different questions and neither one answers
+# for the other.
+# Each list holds two values because a one value list is parsed as an
+# equality and never becomes an IN predicate.
+set names utf8mb3 collate utf8mb3_german2_ci;
+create table t1 (a char(10) character set utf8mb3);
+insert into t1 values (_utf8mb3 0xC3B6),('oe');
+explain extended select * from t1
+where a in ('oe','xx') and a = 'oe' collate utf8mb3_german2_ci;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
+1	SIMPLE	t1	ALL	NULL	NULL	NULL	NULL	2	100.00	Using where
+Warnings:
+Note	1003	select `test`.`t1`.`a` AS `a` from `test`.`t1` where `test`.`t1`.`a` in ('oe','xx') and `test`.`t1`.`a` = 'oe'
+select hex(a) from t1
+where a in ('oe','xx') and a = 'oe' collate utf8mb3_german2_ci;
+hex(a)
+6F65
+# Only the first value of the next list carries the other collation, so
+# the second value on its own would allow the rewrite.  Refusing the
+# whole predicate shows the check runs per value.
+explain extended select * from t1
+where a in ('oe' collate utf8mb3_german2_ci,'xx') and a = 'oe';
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
+1	SIMPLE	t1	ALL	NULL	NULL	NULL	NULL	2	100.00	Using where
+Warnings:
+Note	1003	select `test`.`t1`.`a` AS `a` from `test`.`t1` where `test`.`t1`.`a` = 'oe' and `test`.`t1`.`a` in (<cache>('oe' collate utf8mb3_german2_ci),'xx')
+select hex(a) from t1
+where a in ('oe' collate utf8mb3_german2_ci,'xx') and a = 'oe';
+hex(a)
+6F65
+# With one collation throughout, the same rows let the rewrite happen.
+# The equality on its own matches both rows, so keeping the IN above is
+# what holds the o-umlaut row back.
+explain extended select * from t1 where a in ('oe','xx') and a = 'oe';
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
+1	SIMPLE	t1	ALL	NULL	NULL	NULL	NULL	2	100.00	Using where
+Warnings:
+Note	1003	select `test`.`t1`.`a` AS `a` from `test`.`t1` where `test`.`t1`.`a` = 'oe'
+select hex(a) from t1 where a in ('oe','xx') and a = 'oe';
+hex(a)
+6F65
+select hex(a) from t1 where a = 'oe' collate utf8mb3_german2_ci;
+hex(a)
+C3B6
+6F65
+drop table t1;
+set names default;
+# A constant that stands in for another item is refused.  Comparing the
+# literal 1 against a YEAR column turns it into the value the column
+# would hold, 2001, and the value list is converted the same way.  A
+# clone of that constant carries the literal 1, which matches nothing in
+# the converted list, so the predicant keeps the column.
+# The equality is <=> rather than = so that the multiple equality
+# machinery leaves the condition to this rewrite.
+create table t1 (y year);
+insert into t1 values (2001),(2002),(2003);
+explain extended select * from t1 where y in (1,2) and y <=> 1;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
+1	SIMPLE	t1	ALL	NULL	NULL	NULL	NULL	3	100.00	Using where
+Warnings:
+Note	1003	select `test`.`t1`.`y` AS `y` from `test`.`t1` where `test`.`t1`.`y` in (2001,2002) and `test`.`t1`.`y` <=> 2001
+select * from t1 where y in (1,2) and y <=> 1;
+y
+2001
+select * from t1 where y in (1,2) and y <=> 2;
+y
+2002
+select * from t1 where y in (1,2) and y <=> 3;
+y
+drop table t1;
+# A NULL in the list leaves the predicant alone.  A column in the list
+# does not, and the rewritten predicate still answers correctly.
+create table t1 (v varchar(64), w varchar(64));
+insert into t1 values ('a','a'),('b','b');
+explain extended select * from t1 where v in ('a',NULL) and v = 'b';
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
+1	SIMPLE	NULL	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Impossible WHERE
+Warnings:
+Note	1003	select `test`.`t1`.`v` AS `v`,`test`.`t1`.`w` AS `w` from `test`.`t1` where 0
+select * from t1 where v in ('a',NULL) and v = 'b';
+v	w
+explain extended select * from t1 where v in ('a',w) and v = 'b';
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
+1	SIMPLE	t1	ALL	NULL	NULL	NULL	NULL	2	100.00	Using where
+Warnings:
+Note	1003	select `test`.`t1`.`v` AS `v`,`test`.`t1`.`w` AS `w` from `test`.`t1` where `test`.`t1`.`v` = 'b' and 'b' in ('a',`test`.`t1`.`w`)
+select * from t1 where v in ('a',w) and v = 'b';
+v	w
+b	b
+drop table t1;
+# The rewrite is undone after each execution of a prepared statement
+# and done again on the next, with the parameter values bound for it.
+create table t1 (v varchar(64));
+insert into t1 values ('a'),('b');
+prepare s from 'explain extended
+  select * from t1 where v in (''a'',''b'') and v = ''b''';
+execute s;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
+1	SIMPLE	t1	ALL	NULL	NULL	NULL	NULL	2	100.00	Using where
+Warnings:
+Note	1003	select `test`.`t1`.`v` AS `v` from `test`.`t1` where `test`.`t1`.`v` = 'b'
+execute s;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
+1	SIMPLE	t1	ALL	NULL	NULL	NULL	NULL	2	100.00	Using where
+Warnings:
+Note	1003	select `test`.`t1`.`v` AS `v` from `test`.`t1` where `test`.`t1`.`v` = 'b'
+prepare s from 'select * from t1 where v in (''a'',''b'') and v = ''b''';
+execute s;
+v
+b
+execute s;
+v
+b
+# Parameters in the list make the IN predicate TRUE and then FALSE.
+prepare s from 'explain extended
+  select * from t1 where v in (?,?) and v = ''b''';
+execute s using 'a', 'b';
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
+1	SIMPLE	t1	ALL	NULL	NULL	NULL	NULL	2	100.00	Using where
+Warnings:
+Note	1003	select `test`.`t1`.`v` AS `v` from `test`.`t1` where `test`.`t1`.`v` = 'b'
+execute s using 'a', 'x';
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
+1	SIMPLE	NULL	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Impossible WHERE
+Warnings:
+Note	1003	select `test`.`t1`.`v` AS `v` from `test`.`t1` where 0
+prepare s from 'select * from t1 where v in (?,?) and v = ''b''';
+execute s using 'a', 'b';
+v
+b
+execute s using 'a', 'x';
+v
+execute s using 'a', 'b';
+v
+b
+# A parameter in the equality is cloned with the value bound for each
+# execution.
+prepare s from 'explain extended
+  select * from t1 where v in (''a'',''b'') and v = ?';
+execute s using 'b';
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
+1	SIMPLE	t1	ALL	NULL	NULL	NULL	NULL	2	100.00	Using where
+Warnings:
+Note	1003	select `test`.`t1`.`v` AS `v` from `test`.`t1` where `test`.`t1`.`v` = 'b'
+execute s using 'x';
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
+1	SIMPLE	NULL	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Impossible WHERE
+Warnings:
+Note	1003	select `test`.`t1`.`v` AS `v` from `test`.`t1` where 0
+prepare s from 'select * from t1 where v in (''a'',''b'') and v = ?';
+execute s using 'b';
+v
+b
+execute s using 'x';
+v
+execute s using 'a';
+v
+a
+deallocate prepare s;
+drop table t1;
+#
+# End of 11.8 tests
+#
--- a/mysql-test/main/func_in.test
+++ b/mysql-test/main/func_in.test
@@ -936,3 +936,119 @@ drop table t1;
 --echo #
 --echo # End of 10.6 tests
 --echo #
+
+--echo #
+--echo # MDEV-35845 WHERE COL IN (item0, item1, ..., itemN) AND COL = item1
+--echo # Optimization
+--echo #
+
+create table t1 (v varchar(64), t text, c char(32));
+insert into t1 values ('a','a','a'),('b','b','b');
+explain extended select * from t1 where v in ('a','b') and v = 'b';
+explain extended select * from t1 where t in ('a','b') and t = 'b';
+explain extended select * from t1 where c in ('a','b') and c = 'b';
+explain extended select * from t1 where v not in ('a','b') and v = 'b';
+select * from t1 where v in ('a','b') and v = 'b';
+select * from t1 where v in ('a','x') and v = 'b';
+select * from t1 where v not in ('a','b') and v = 'b';
+drop table t1;
+
+--echo # The predicant is left alone when the IN predicate and the equality
+--echo # compare with different collations.  Under utf8mb3_german2_ci the
+--echo # o-umlaut row matches 'oe', under utf8mb3_general_ci it does not, so
+--echo # the two predicates ask different questions and neither one answers
+--echo # for the other.
+--echo # Each list holds two values because a one value list is parsed as an
+--echo # equality and never becomes an IN predicate.
+
+set names utf8mb3 collate utf8mb3_german2_ci;
+create table t1 (a char(10) character set utf8mb3);
+insert into t1 values (_utf8mb3 0xC3B6),('oe');
+explain extended select * from t1
+  where a in ('oe','xx') and a = 'oe' collate utf8mb3_german2_ci;
+select hex(a) from t1
+  where a in ('oe','xx') and a = 'oe' collate utf8mb3_german2_ci;
+--echo # Only the first value of the next list carries the other collation, so
+--echo # the second value on its own would allow the rewrite.  Refusing the
+--echo # whole predicate shows the check runs per value.
+explain extended select * from t1
+  where a in ('oe' collate utf8mb3_german2_ci,'xx') and a = 'oe';
+select hex(a) from t1
+  where a in ('oe' collate utf8mb3_german2_ci,'xx') and a = 'oe';
+--echo # With one collation throughout, the same rows let the rewrite happen.
+--echo # The equality on its own matches both rows, so keeping the IN above is
+--echo # what holds the o-umlaut row back.
+explain extended select * from t1 where a in ('oe','xx') and a = 'oe';
+select hex(a) from t1 where a in ('oe','xx') and a = 'oe';
+select hex(a) from t1 where a = 'oe' collate utf8mb3_german2_ci;
+drop table t1;
+set names default;
+
+--echo # A constant that stands in for another item is refused.  Comparing the
+--echo # literal 1 against a YEAR column turns it into the value the column
+--echo # would hold, 2001, and the value list is converted the same way.  A
+--echo # clone of that constant carries the literal 1, which matches nothing in
+--echo # the converted list, so the predicant keeps the column.
+--echo # The equality is <=> rather than = so that the multiple equality
+--echo # machinery leaves the condition to this rewrite.
+
+create table t1 (y year);
+insert into t1 values (2001),(2002),(2003);
+explain extended select * from t1 where y in (1,2) and y <=> 1;
+select * from t1 where y in (1,2) and y <=> 1;
+select * from t1 where y in (1,2) and y <=> 2;
+select * from t1 where y in (1,2) and y <=> 3;
+drop table t1;
+
+--echo # A NULL in the list leaves the predicant alone.  A column in the list
+--echo # does not, and the rewritten predicate still answers correctly.
+
+create table t1 (v varchar(64), w varchar(64));
+insert into t1 values ('a','a'),('b','b');
+explain extended select * from t1 where v in ('a',NULL) and v = 'b';
+select * from t1 where v in ('a',NULL) and v = 'b';
+explain extended select * from t1 where v in ('a',w) and v = 'b';
+select * from t1 where v in ('a',w) and v = 'b';
+drop table t1;
+
+--echo # The rewrite is undone after each execution of a prepared statement
+--echo # and done again on the next, with the parameter values bound for it.
+
+create table t1 (v varchar(64));
+insert into t1 values ('a'),('b');
+
+prepare s from 'explain extended
+  select * from t1 where v in (''a'',''b'') and v = ''b''';
+execute s;
+execute s;
+prepare s from 'select * from t1 where v in (''a'',''b'') and v = ''b''';
+execute s;
+execute s;
+
+--echo # Parameters in the list make the IN predicate TRUE and then FALSE.
+prepare s from 'explain extended
+  select * from t1 where v in (?,?) and v = ''b''';
+execute s using 'a', 'b';
+execute s using 'a', 'x';
+prepare s from 'select * from t1 where v in (?,?) and v = ''b''';
+execute s using 'a', 'b';
+execute s using 'a', 'x';
+execute s using 'a', 'b';
+
+--echo # A parameter in the equality is cloned with the value bound for each
+--echo # execution.
+prepare s from 'explain extended
+  select * from t1 where v in (''a'',''b'') and v = ?';
+execute s using 'b';
+execute s using 'x';
+prepare s from 'select * from t1 where v in (''a'',''b'') and v = ?';
+execute s using 'b';
+execute s using 'x';
+execute s using 'a';
+
+deallocate prepare s;
+drop table t1;
+
+--echo #
+--echo # End of 11.8 tests
+--echo #
--- a/mysql-test/main/having.result
+++ b/mysql-test/main/having.result
@@ -713,7 +713,7 @@ select * from mysql.help_topic where example = 'foo' having description is null;
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
 1	SIMPLE	NULL	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Impossible HAVING
 Warnings:
-Note	1003	select `mysql`.`help_topic`.`help_topic_id` AS `help_topic_id`,`mysql`.`help_topic`.`name` AS `name`,`mysql`.`help_topic`.`help_category_id` AS `help_category_id`,`mysql`.`help_topic`.`description` AS `description`,`mysql`.`help_topic`.`example` AS `example`,`mysql`.`help_topic`.`url` AS `url` from `mysql`.`help_topic` where `mysql`.`help_topic`.`example` = 'foo' having 0
+Note	1003	select `mysql`.`help_topic`.`help_topic_id` AS `help_topic_id`,`mysql`.`help_topic`.`name` AS `name`,`mysql`.`help_topic`.`help_category_id` AS `help_category_id`,`mysql`.`help_topic`.`description` AS `description`,`mysql`.`help_topic`.`example` AS `example`,`mysql`.`help_topic`.`url` AS `url` from `mysql`.`help_topic` where multiple equal('foo', `mysql`.`help_topic`.`example`) having 0
 select * from mysql.help_topic where example = 'foo' having description is null;
 help_topic_id	name	help_category_id	description	example	url
 #
--- a/mysql-test/main/information_schema.result
+++ b/mysql-test/main/information_schema.result
@@ -1734,7 +1734,7 @@ from information_schema.tables a, information_schema.columns b
 where a.table_name='t1' and a.table_schema='test' and b.table_name=a.table_name;
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	SIMPLE	a	ALL	NULL	TABLE_SCHEMA,TABLE_NAME	NULL	NULL	NULL	Using where; Skip_open_table; Scanned 0 databases
-1	SIMPLE	b	ALL	NULL	NULL	NULL	NULL	NULL	Using where; Open_frm_only; Scanned all databases; Using join buffer (flat, BNL join)
+1	SIMPLE	b	ALL	NULL	TABLE_NAME	NULL	NULL	NULL	Using where; Open_frm_only; Scanned 1 database; Using join buffer (flat, BNL join)
 SELECT * FROM INFORMATION_SCHEMA.SCHEMATA
 WHERE SCHEMA_NAME = 'mysqltest';
 CATALOG_NAME	SCHEMA_NAME	DEFAULT_CHARACTER_SET_NAME	DEFAULT_COLLATION_NAME	SQL_PATH	SCHEMA_COMMENT
--- a/mysql-test/main/innodb_ext_key.result
+++ b/mysql-test/main/innodb_ext_key.result
@@ -779,7 +779,7 @@ EXPLAIN
          "rows": 1,
          "cost": "COST_REPLACED",
          "filtered": 100,
-          "index_condition": "t1.pk1 <= 5 and t1.pk2 <= 5 and t1.f2 = 'abc'",
+          "index_condition": "t1.f2 = 'abc' and t1.pk1 <= 5 and t1.pk2 <= 5",
          "attached_condition": "t1.f1 <= '3'"
        }
      }
@@ -816,7 +816,7 @@ EXPLAIN
          "rows": 1,
          "cost": "COST_REPLACED",
          "filtered": 100,
-          "index_condition": "t1.f2 <= 5 and t1.pk2 <= 5 and t1.pk1 = 'abc'",
+          "index_condition": "t1.pk1 = 'abc' and t1.f2 <= 5 and t1.pk2 <= 5",
          "attached_condition": "t1.f1 <= '3'"
        }
      }
--- a/mysql-test/main/join.result
+++ b/mysql-test/main/join.result
@@ -759,10 +759,6 @@ from information_schema.statistics join information_schema.columns using(table_n
 TABLE_NAME	COLUMN_NAME	TABLE_CATALOG	TABLE_SCHEMA	NON_UNIQUE	INDEX_SCHEMA	INDEX_NAME	SEQ_IN_INDEX	COLLATION	SUB_PART	PACKED	NULLABLE	INDEX_TYPE	COMMENT	TABLE_CATALOG	TABLE_SCHEMA	COLUMN_DEFAULT	IS_NULLABLE	DATA_TYPE	CHARACTER_MAXIMUM_LENGTH	CHARACTER_OCTET_LENGTH	NUMERIC_PRECISION	NUMERIC_SCALE	CHARACTER_SET_NAME	COLLATION_NAME	COLUMN_TYPE	COLUMN_KEY	EXTRA	COLUMN_COMMENT
 global_priv	Host	def	mysql	0	mysql	PRIMARY	1	A	NULL	NULL		BTREE		def	mysql	''	NO	char	255	765	NULL	NULL	utf8mb3	utf8mb3_bin	char(255)	PRI		
 global_priv	User	def	mysql	0	mysql	PRIMARY	2	A	NULL	NULL		BTREE		def	mysql	''	NO	char	128	384	NULL	NULL	utf8mb3	utf8mb3_bin	char(128)	PRI		
-Warnings:
-Warning	1286	Unknown storage engine 'InnoDB'
-Warning	1286	Unknown storage engine 'InnoDB'
-Warning	1286	Unknown storage engine 'InnoDB'
 drop table t1;
 drop table t2;
 drop table t3;
--- a/mysql-test/main/mrr_derived_crash_4610.result
+++ b/mysql-test/main/mrr_derived_crash_4610.result
@@ -8,7 +8,7 @@ explain select 1 from
 join t1 on f1 = f3 where f3 = 'aaaa' order by val;
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	PRIMARY	t1	const	PRIMARY	PRIMARY	12	const	1	
-1	PRIMARY	<derived2>	ref	key0	key0	13	const	0	Using where; Using filesort
+1	PRIMARY	<derived2>	ALL	NULL	NULL	NULL	NULL	2	Using where; Using filesort
 2	DERIVED	t4	ALL	NULL	NULL	NULL	NULL	1	
 2	DERIVED	t2	ALL	NULL	NULL	NULL	NULL	1	Using join buffer (flat, BNL join)
 2	DERIVED	t3	ALL	NULL	NULL	NULL	NULL	1	Using where; Using join buffer (incremental, BNL join)
--- a/mysql-test/main/ps.result
+++ b/mysql-test/main/ps.result
@@ -1209,24 +1209,12 @@ prepare my_stmt from @aux;
 execute my_stmt;
 COUNT(*)
 47
-Warnings:
-Warning	1286	Unknown storage engine 'InnoDB'
-Warning	1286	Unknown storage engine 'InnoDB'
-Warning	1286	Unknown storage engine 'InnoDB'
 execute my_stmt;
 COUNT(*)
 47
-Warnings:
-Warning	1286	Unknown storage engine 'InnoDB'
-Warning	1286	Unknown storage engine 'InnoDB'
-Warning	1286	Unknown storage engine 'InnoDB'
 execute my_stmt;
 COUNT(*)
 47
-Warnings:
-Warning	1286	Unknown storage engine 'InnoDB'
-Warning	1286	Unknown storage engine 'InnoDB'
-Warning	1286	Unknown storage engine 'InnoDB'
 deallocate prepare my_stmt;
 drop procedure if exists p1|
 drop table if exists t1|
--- a/mysql-test/main/rowid_filter_innodb.result
+++ b/mysql-test/main/rowid_filter_innodb.result
@@ -3156,7 +3156,7 @@ id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
 1	SIMPLE	a	ref	PRIMARY,acei_aclid	acei_aclid	8	test.t.id	1	100.00	Using where
 1	SIMPLE	fi	ref	filt_aceid,filt_fh	filt_aceid	8	test.a.id	24	14.46	Using where
 Warnings:
-Note	1003	select `test`.`t`.`id` AS `id`,`test`.`fi`.`id` AS `id`,`test`.`fi`.`aceid` AS `aceid`,`test`.`fi`.`clid` AS `clid`,`test`.`fi`.`fh` AS `fh` from `test`.`acli` `t` join `test`.`acei` `a` join `test`.`filt` `fi` where `test`.`t`.`tp` = 121 and `test`.`a`.`atp` = 1 and `test`.`fi`.`aceid` = `test`.`a`.`id` and `test`.`a`.`aclid` = `test`.`t`.`id` and `test`.`t`.`rid` = 'B5FCC8C7111E4E3CBC21AAF5012F59C2' and `test`.`fi`.`fh` in (6311439873746261694,-397087483897438286,8518228073041491534,-5420422472375069774)
+Note	1003	select `test`.`t`.`id` AS `id`,`test`.`fi`.`id` AS `id`,`test`.`fi`.`aceid` AS `aceid`,`test`.`fi`.`clid` AS `clid`,`test`.`fi`.`fh` AS `fh` from `test`.`acli` `t` join `test`.`acei` `a` join `test`.`filt` `fi` where `test`.`t`.`rid` = 'B5FCC8C7111E4E3CBC21AAF5012F59C2' and `test`.`t`.`tp` = 121 and `test`.`a`.`atp` = 1 and `test`.`fi`.`aceid` = `test`.`a`.`id` and `test`.`a`.`aclid` = `test`.`t`.`id` and `test`.`fi`.`fh` in (6311439873746261694,-397087483897438286,8518228073041491534,-5420422472375069774)
 set statement optimizer_switch='rowid_filter=off' for select t.id, fi.*
 from (acli t inner join acei a on a.aclid = t.id)
 inner join filt fi on a.id = fi.aceid
@@ -3213,7 +3213,7 @@ id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
 1	SIMPLE	a	ref	PRIMARY,acei_aclid	acei_aclid	8	test.t.id	1	100.00	Using where
 1	SIMPLE	fi	ref|filter	filt_aceid,filt_fh	filt_aceid|filt_fh	8|8	test.a.id	24 (14%)	14.46	Using where; Using rowid filter
 Warnings:
-Note	1003	select `test`.`t`.`id` AS `id`,`test`.`fi`.`id` AS `id`,`test`.`fi`.`aceid` AS `aceid`,`test`.`fi`.`clid` AS `clid`,`test`.`fi`.`fh` AS `fh` from `test`.`acli` `t` join `test`.`acei` `a` join `test`.`filt` `fi` where `test`.`t`.`tp` = 121 and `test`.`a`.`atp` = 1 and `test`.`fi`.`aceid` = `test`.`a`.`id` and `test`.`a`.`aclid` = `test`.`t`.`id` and `test`.`t`.`rid` = 'B5FCC8C7111E4E3CBC21AAF5012F59C2' and `test`.`fi`.`fh` in (6311439873746261694,-397087483897438286,8518228073041491534,-5420422472375069774)
+Note	1003	select `test`.`t`.`id` AS `id`,`test`.`fi`.`id` AS `id`,`test`.`fi`.`aceid` AS `aceid`,`test`.`fi`.`clid` AS `clid`,`test`.`fi`.`fh` AS `fh` from `test`.`acli` `t` join `test`.`acei` `a` join `test`.`filt` `fi` where `test`.`t`.`rid` = 'B5FCC8C7111E4E3CBC21AAF5012F59C2' and `test`.`t`.`tp` = 121 and `test`.`a`.`atp` = 1 and `test`.`fi`.`aceid` = `test`.`a`.`id` and `test`.`a`.`aclid` = `test`.`t`.`id` and `test`.`fi`.`fh` in (6311439873746261694,-397087483897438286,8518228073041491534,-5420422472375069774)
 set statement optimizer_switch='rowid_filter=on' for select t.id, fi.*
 from (acli t inner join acei a on a.aclid = t.id)
 inner join filt fi on a.id = fi.aceid
@@ -3272,7 +3272,7 @@ id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
 1	SIMPLE	a	ref	PRIMARY,acei_aclid	acei_aclid	8	test.t.id	1	100.00	Using where; Using join buffer (flat, BKA join); Rowid-ordered scan
 1	SIMPLE	fi	ref	filt_aceid,filt_fh	filt_aceid	8	test.a.id	24	14.46	Using where; Using join buffer (incremental, BKA join); Rowid-ordered scan
 Warnings:
-Note	1003	select `test`.`t`.`id` AS `id`,`test`.`fi`.`id` AS `id`,`test`.`fi`.`aceid` AS `aceid`,`test`.`fi`.`clid` AS `clid`,`test`.`fi`.`fh` AS `fh` from `test`.`acli` `t` join `test`.`acei` `a` join `test`.`filt` `fi` where `test`.`t`.`tp` = 121 and `test`.`a`.`atp` = 1 and `test`.`fi`.`aceid` = `test`.`a`.`id` and `test`.`a`.`aclid` = `test`.`t`.`id` and `test`.`t`.`rid` = 'B5FCC8C7111E4E3CBC21AAF5012F59C2' and `test`.`fi`.`fh` in (6311439873746261694,-397087483897438286,8518228073041491534,-5420422472375069774)
+Note	1003	select `test`.`t`.`id` AS `id`,`test`.`fi`.`id` AS `id`,`test`.`fi`.`aceid` AS `aceid`,`test`.`fi`.`clid` AS `clid`,`test`.`fi`.`fh` AS `fh` from `test`.`acli` `t` join `test`.`acei` `a` join `test`.`filt` `fi` where `test`.`t`.`rid` = 'B5FCC8C7111E4E3CBC21AAF5012F59C2' and `test`.`t`.`tp` = 121 and `test`.`a`.`atp` = 1 and `test`.`fi`.`aceid` = `test`.`a`.`id` and `test`.`a`.`aclid` = `test`.`t`.`id` and `test`.`fi`.`fh` in (6311439873746261694,-397087483897438286,8518228073041491534,-5420422472375069774)
 set statement optimizer_switch='rowid_filter=off' for select t.id, fi.*
 from (acli t inner join acei a on a.aclid = t.id)
 inner join filt fi on a.id = fi.aceid
@@ -3329,7 +3329,7 @@ id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
 1	SIMPLE	a	ref	PRIMARY,acei_aclid	acei_aclid	8	test.t.id	1	100.00	Using where; Using join buffer (flat, BKA join); Rowid-ordered scan
 1	SIMPLE	fi	ref|filter	filt_aceid,filt_fh	filt_aceid|filt_fh	8|8	test.a.id	24 (14%)	14.46	Using where; Using join buffer (incremental, BKA join); Rowid-ordered scan; Using rowid filter
 Warnings:
-Note	1003	select `test`.`t`.`id` AS `id`,`test`.`fi`.`id` AS `id`,`test`.`fi`.`aceid` AS `aceid`,`test`.`fi`.`clid` AS `clid`,`test`.`fi`.`fh` AS `fh` from `test`.`acli` `t` join `test`.`acei` `a` join `test`.`filt` `fi` where `test`.`t`.`tp` = 121 and `test`.`a`.`atp` = 1 and `test`.`fi`.`aceid` = `test`.`a`.`id` and `test`.`a`.`aclid` = `test`.`t`.`id` and `test`.`t`.`rid` = 'B5FCC8C7111E4E3CBC21AAF5012F59C2' and `test`.`fi`.`fh` in (6311439873746261694,-397087483897438286,8518228073041491534,-5420422472375069774)
+Note	1003	select `test`.`t`.`id` AS `id`,`test`.`fi`.`id` AS `id`,`test`.`fi`.`aceid` AS `aceid`,`test`.`fi`.`clid` AS `clid`,`test`.`fi`.`fh` AS `fh` from `test`.`acli` `t` join `test`.`acei` `a` join `test`.`filt` `fi` where `test`.`t`.`rid` = 'B5FCC8C7111E4E3CBC21AAF5012F59C2' and `test`.`t`.`tp` = 121 and `test`.`a`.`atp` = 1 and `test`.`fi`.`aceid` = `test`.`a`.`id` and `test`.`a`.`aclid` = `test`.`t`.`id` and `test`.`fi`.`fh` in (6311439873746261694,-397087483897438286,8518228073041491534,-5420422472375069774)
 set statement optimizer_switch='rowid_filter=on' for select t.id, fi.*
 from (acli t inner join acei a on a.aclid = t.id)
 inner join filt fi on a.id = fi.aceid
@@ -3424,7 +3424,7 @@ ANALYZE
          "r_engine_stats": REPLACED,
          "filtered": 100,
          "r_total_filtered": 100,
-          "attached_condition": "t.tp = 121 and t.rid = 'B5FCC8C7111E4E3CBC21AAF5012F59C2'",
+          "attached_condition": "t.rid = 'B5FCC8C7111E4E3CBC21AAF5012F59C2' and t.tp = 121",
          "r_filtered": 100,
          "using_index": true
        }
--- a/mysql-test/main/sargable_casefold.result
+++ b/mysql-test/main/sargable_casefold.result
@@ -206,7 +206,7 @@ select a from t3 ignore index(a) where a=b and upper(b)='ABC';
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
 1	SIMPLE	t3	ref	b	b	99	const	1	100.00	Using index condition; Using where
 Warnings:
-Note	1003	select `test`.`t3`.`a` AS `a` from `test`.`t3` IGNORE INDEX (`a`) where `test`.`t3`.`a` = `test`.`t3`.`b` and `test`.`t3`.`b` = 'ABC'
+Note	1003	select `test`.`t3`.`a` AS `a` from `test`.`t3` IGNORE INDEX (`a`) where `test`.`t3`.`b` = 'ABC' and `test`.`t3`.`a` = 'ABC'
 #
 # Check that rewrite isn't applied for non-applicable collations
 #
--- a/sql/field.cc
+++ b/sql/field.cc
@@ -2403,16 +2403,7 @@ Field_str::Field_str(uchar *ptr_arg,uint32 len_arg, uchar *null_ptr_arg,

 bool Field_str::test_if_equality_guarantees_uniqueness(const Item *item) const
 {
-  /*
-    Can't guarantee uniqueness when comparing a CHAR/VARCHAR/TEXT,
-    BINARY/VARBINARY/BLOB, ENUM,SET columns to an item with cmp_type()
-    of INT_RESULT, DOUBLE_RESULT, DECIMAL_RESULT or TIME_RESULT.
-    Example:
-      SELECT * FROM t1 WHERE varchar_column=DATE'2001-01-01'
-    return non-unuque values, e.g. '2001-01-01' and '2001-01-01x'.
-  */
-  if (!field_charset()->propagate(0, 0) ||
-      item->cmp_type() != STRING_RESULT)
+  if (item->cmp_type() != STRING_RESULT)
    return false;
  /*
    Can't guarantee uniqueness when comparing to
@@ -7614,6 +7605,56 @@ uint32 Field_longstr::max_data_length() const
 }


+/*
+  Convert a constant held by an Item_equal into this field's character set.
+
+  @param ctx  The comparison context.  ctx.compare_collation() is the
+              collation the Item_equal compares under, and the constant's
+              bytes are in that collation's character set.
+
+  Item_equal::add_const() and eliminate_item_equal() assume that every
+  constant held by an Item_equal is directly comparable with every field
+  member.  A utf8mb3_general_ci field and a utf8mb4_general_ci field can
+  share one Item_equal through charset narrowing, so when an equality
+  "utf8mb3_field = utf8mb4_constant" is manufactured for such a member the
+  constant has to be narrowed first.  Narrowing maps characters outside the
+  BMP to U+FFFD, which is what utf8mb4_general_ci compares them as.
+
+  @return  the constant itself when its character set is the field's,
+           a new string literal in the field's character set,
+           or NULL when the constant cannot be represented in the field's
+           character set, which makes the equality unusable.
+*/
+Item *Field_longstr::get_equal_const_item(THD *thd, const Context &ctx,
+                                          Item *const_item)
+{
+  if (ctx.subst_constraint() != ANY_SUBST ||
+      const_item->cmp_type() != STRING_RESULT)
+    return const_item;
+  CHARSET_INFO *from= ctx.compare_collation();
+  if (!from || my_charset_same(charset(), from))
+    return const_item;
+
+  StringBuffer<MAX_FIELD_WIDTH> buf;
+  String *str= const_item->val_str(&buf);
+  if (!str)
+    return const_item;                          // NULL, nothing to convert
+
+  CHARSET_INFO *conv_cs= Utf8_narrow::should_do_narrowing(this, from) ?
+                         utf8mb3_from_mb4.charset() : charset();
+  uint errors= 0;
+  StringBuffer<MAX_FIELD_WIDTH> conv;
+  if (conv.copy(str->ptr(), str->length(), from, conv_cs, &errors) || errors)
+    return NULL;
+
+  char *copy= thd->strmake(conv.ptr(), conv.length());
+  if (!copy)
+    return NULL;
+  return new (thd->mem_root) Item_string(thd, copy, conv.length(), charset(),
+                                         const_item->collation.derivation);
+}
+
+
 Data_type_compatibility
 Field_longstr::cmp_to_string_with_same_collation(const Item_bool_func *cond,
                                                 const Item *item) const
--- a/sql/field.h
+++ b/sql/field.h
@@ -2345,6 +2345,8 @@ public:
    return bitmap_is_set(table->write_set, field_index);
  }
  bool match_collation_to_optimize_range() const { return true; }
+  Item *get_equal_const_item(THD *thd, const Context &ctx, Item *const_item)
+    override;

  Data_type_compatibility can_optimize_keypart_ref(const Item_bool_func *cond,
                                                   const Item *item)
--- a/sql/sql_select.cc
+++ b/sql/sql_select.cc
@@ -19126,6 +19126,22 @@ Item *eliminate_item_equal(THD *thd, COND *cond, COND_EQUAL *upper_levels,
      */
      Item *head_item= (!item_const && current_sjm && 
                        current_sjm_head != field_item) ? current_sjm_head: head;
+      if (item_const)
+      {
+        /*
+          The constant is held in the comparison collation of the multiple
+          equality.  A member that joined it through charset narrowing has a
+          different character set, so convert the constant for that member.
+        */
+        Field *field= it.get_curr_field();
+        head_item= field->get_equal_const_item(thd,
+                     Item::Context(Item::ANY_SUBST,
+                                   item_equal->compare_type_handler(),
+                                   item_equal->compare_collation()),
+                     item_const);
+        if (!head_item)
+          return 0;
+      }
      eq_item= new (thd->mem_root) Item_func_eq(thd, field_item, head_item);

      if (!eq_item || eq_item->set_cmp_func(thd))
--- a/storage/spider/mysql-test/spider/bugfix/r/mdev_27172,usual_handler.rdiff
+++ b/storage/spider/mysql-test/spider/bugfix/r/mdev_27172,usual_handler.rdiff
@@ -1,12 +1,12 @@
--- ../src/storage/spider/mysql-test/spider/bugfix/r/mdev_27172.result	2024-11-15 17:14:27.541903833 +1100
-+++ ../src/storage/spider/mysql-test/spider/bugfix/r/mdev_27172.reject	2025-10-22 17:40:25.831151167 +1100
-@@ -66,6 +66,9 @@
+--- storage/spider/mysql-test/spider/bugfix/r/mdev_27172.result	2025-11-13 13:38:25.377373719 +1300
+++ storage/spider/mysql-test/spider/bugfix/r/mdev_27172,usual_handler.reject	2026-10-15 14:40:08.495538888 +1300
+@@ -72,6 +72,9 @@
 connection child2_1;
 SELECT argument FROM mysql.general_log WHERE argument LIKE 'select `id`,`greeting` from %';
 argument
-+select `id`,`greeting` from `auto_test_remote`.`tbl_a` where `greeting` = 'Aloha!' and ((`greeting` = 'Aloha!') and ((case `greeting` when 'Aloha!' then _latin1'one' else _latin1'more' end) = _latin1'one'))
-+select `id`,`greeting` from `auto_test_remote`.`tbl_b` where `greeting` like 'Aloha%' and ((`greeting` = 'Aloha!') and ((case `greeting` when 'Aloha!' then _latin1'one' else _latin1'more' end) = _latin1'one'))
-+select `id`,`greeting` from `auto_test_remote`.`tbl_c` where `greeting` like 'Aloha%' and ((`greeting` = 'Aloha!') and ((case `greeting` when 'Aloha!' then _latin1'one' else _latin1'more' end) = _latin1'one'))
+select `id`,`greeting` from `auto_test_remote`.`tbl_a` where `greeting` = 'Aloha!' and (`greeting` = 'Aloha!')
+select `id`,`greeting` from `auto_test_remote`.`tbl_b` where `greeting` like 'Aloha%' and (`greeting` = 'Aloha!')
+select `id`,`greeting` from `auto_test_remote`.`tbl_c` where `greeting` like 'Aloha%' and (`greeting` = 'Aloha!')
 connection child2_1;
 SET @@global.general_log = @general_log_backup;
 SET @@global.log_output = @log_output_backup;