mysql · akcube · Nov 21, 2025
diff --git a/mysql-test/r/group_skip_scan.result b/mysql-test/r/group_skip_scan.result
@@ -4316,10 +4316,8 @@ INSERT INTO t1 VALUES (NULL, 1);
 INSERT INTO t1 VALUES (NULL, 2);
 EXPLAIN FORMAT=TREE SELECT MIN(f2) FROM t1 WHERE f1 IS NULL GROUP BY f1;
 EXPLAIN
--> Table scan on <temporary>  (rows=1)
-    -> Temporary table with deduplication  (rows=1)
-        -> Filter: (t1.f1 is null)  (rows=1)
-            -> Covering index skip scan for grouping on t1 using f1 over (f1 = NULL)  (rows=1)
+-> Filter: (t1.f1 is null)  (rows=1)
+    -> Covering index skip scan for grouping on t1 using f1 over (f1 = NULL)  (rows=1)
 
 SELECT MIN(f2) FROM t1 WHERE f1 IS NULL GROUP BY f1;
 MIN(f2)

diff --git a/mysql-test/r/order_by_all.result b/mysql-test/r/order_by_all.result
@@ -392,7 +392,7 @@ a	b	c
 1	NULL	b
 explain select * from t1 where a = 1 and b is null order by a desc, b desc;
 id	select_type	table	partitions	type	possible_keys	key	key_len	ref	rows	filtered	Extra
-1	SIMPLE	t1	NULL	ref	a	a	9	const,const	2	100.00	Using where; Using index; Using filesort
+1	SIMPLE	t1	NULL	ref	a	a	9	const,const	2	100.00	Using where; Using index
 Warnings:
 Note	1003	/* select#1 */ select `test`.`t1`.`a` AS `a`,`test`.`t1`.`b` AS `b`,`test`.`t1`.`c` AS `c` from `test`.`t1` where ((`test`.`t1`.`a` = 1) and (`test`.`t1`.`b` is null)) order by `test`.`t1`.`a` desc,`test`.`t1`.`b` desc
 select * from t1 where a = 1 and b is null order by a desc, b desc;
@@ -411,7 +411,7 @@ Warnings:
 Note	1003	/* select#1 */ select `test`.`t1`.`a` AS `a`,`test`.`t1`.`b` AS `b`,`test`.`t1`.`c` AS `c` from `test`.`t1` where ((`test`.`t1`.`a` = 2) and (`test`.`t1`.`b` > 0)) order by `test`.`t1`.`a` desc,`test`.`t1`.`b` desc
 explain select * from t1 where a = 2 and b is null order by a desc,b desc;
 id	select_type	table	partitions	type	possible_keys	key	key_len	ref	rows	filtered	Extra
-1	SIMPLE	t1	NULL	ref	a	a	9	const,const	1	100.00	Using where; Using index; Using filesort
+1	SIMPLE	t1	NULL	ref	a	a	9	const,const	1	100.00	Using where; Using index
 Warnings:
 Note	1003	/* select#1 */ select `test`.`t1`.`a` AS `a`,`test`.`t1`.`b` AS `b`,`test`.`t1`.`c` AS `c` from `test`.`t1` where ((`test`.`t1`.`a` = 2) and (`test`.`t1`.`b` is null)) order by `test`.`t1`.`a` desc,`test`.`t1`.`b` desc
 explain select * from t1 where a = 2 and (b is null or b > 0) order by a

diff --git a/mysql-test/r/order_by_icp_mrr.result b/mysql-test/r/order_by_icp_mrr.result
@@ -392,7 +392,7 @@ a	b	c
 1	NULL	b
 explain select * from t1 where a = 1 and b is null order by a desc, b desc;
 id	select_type	table	partitions	type	possible_keys	key	key_len	ref	rows	filtered	Extra
-1	SIMPLE	t1	NULL	ref	a	a	9	const,const	2	100.00	Using where; Using index; Using filesort
+1	SIMPLE	t1	NULL	ref	a	a	9	const,const	2	100.00	Using where; Using index
 Warnings:
 Note	1003	/* select#1 */ select `test`.`t1`.`a` AS `a`,`test`.`t1`.`b` AS `b`,`test`.`t1`.`c` AS `c` from `test`.`t1` where ((`test`.`t1`.`a` = 1) and (`test`.`t1`.`b` is null)) order by `test`.`t1`.`a` desc,`test`.`t1`.`b` desc
 select * from t1 where a = 1 and b is null order by a desc, b desc;
@@ -411,7 +411,7 @@ Warnings:
 Note	1003	/* select#1 */ select `test`.`t1`.`a` AS `a`,`test`.`t1`.`b` AS `b`,`test`.`t1`.`c` AS `c` from `test`.`t1` where ((`test`.`t1`.`a` = 2) and (`test`.`t1`.`b` > 0)) order by `test`.`t1`.`a` desc,`test`.`t1`.`b` desc
 explain select * from t1 where a = 2 and b is null order by a desc,b desc;
 id	select_type	table	partitions	type	possible_keys	key	key_len	ref	rows	filtered	Extra
-1	SIMPLE	t1	NULL	ref	a	a	9	const,const	1	100.00	Using where; Using index; Using filesort
+1	SIMPLE	t1	NULL	ref	a	a	9	const,const	1	100.00	Using where; Using index
 Warnings:
 Note	1003	/* select#1 */ select `test`.`t1`.`a` AS `a`,`test`.`t1`.`b` AS `b`,`test`.`t1`.`c` AS `c` from `test`.`t1` where ((`test`.`t1`.`a` = 2) and (`test`.`t1`.`b` is null)) order by `test`.`t1`.`a` desc,`test`.`t1`.`b` desc
 explain select * from t1 where a = 2 and (b is null or b > 0) order by a

diff --git a/mysql-test/r/order_by_isnull.result b/mysql-test/r/order_by_isnull.result
@@ -0,0 +1,259 @@
+#
+# Bug#119442: Optimizer doesn't simplify ORDER BY when field IS NULL
+#
+DROP TABLE IF EXISTS t1;
+CREATE TABLE t1 (
+id INT PRIMARY KEY AUTO_INCREMENT,
+category_id INT NOT NULL,
+nullable_date DATETIME DEFAULT NULL,
+created_by VARCHAR(50),
+status VARCHAR(20),
+priority TINYINT,
+item_name VARCHAR(100),
+description VARCHAR(200),
+KEY idx_covering (category_id, nullable_date, created_by, status, priority, item_name, description)
+) ENGINE=InnoDB;
+INSERT INTO t1 (category_id, nullable_date, created_by, status, priority, item_name, description) VALUES
+(100, NULL, 'User1', 'Active', 0, 'Item A', 'Description 1'),
+(100, NULL, 'User1', 'Active', 0, 'Item B', 'Description 2'),
+(100, NULL, 'User1', 'Active', 0, 'Item C', 'Description 3'),
+(100, NULL, 'User1', 'Pending', 0, 'Item D', 'Description 4'),
+(100, '2024-01-01 10:00:00', 'User1', 'Active', 0, 'Item E', 'Description 5'),
+(200, NULL, 'User2', 'Active', 1, 'Item F', 'Description 6'),
+(200, NULL, 'User3', 'Pending', 0, 'Item G', 'Description 7');
+ANALYZE TABLE t1;
+Table	Op	Msg_type	Msg_text
+test.t1	analyze	status	OK
+#
+# Test 1: Basic IS NULL with ORDER BY - demonstrating covering index lookup
+# Covering index is used for IS NULL lookup (category_id, nullable_date)
+# but filesort still needed for item_name since intermediate fields aren't constant
+#
+EXPLAIN FORMAT=TREE
+SELECT id, category_id, nullable_date, item_name
+FROM t1 FORCE INDEX(idx_covering)
+WHERE category_id = 100 AND nullable_date IS NULL
+ORDER BY category_id, nullable_date, item_name;
+EXPLAIN
+-> Sort: t1.item_name  (cost=0.775 rows=4)
+    -> Filter: (t1.nullable_date is null)  (cost=0.775 rows=4)
+        -> Covering index lookup on t1 using idx_covering (category_id = 100, nullable_date = NULL)  (cost=0.775 rows=4)
+
+#
+# Test 2: Compound index with IS NULL - demonstrating NO filesort
+# Unlike Test 1, all intermediate index fields are constant, allowing
+# the index to provide ordering for item_name without filesort
+#
+EXPLAIN FORMAT=TREE
+SELECT id, category_id, status, priority, item_name, description
+FROM t1 FORCE INDEX(idx_covering)
+WHERE category_id = 100
+AND nullable_date IS NULL
+AND created_by = 'User1'
+  AND status = 'Active'
+  AND priority = 0
+AND item_name >= 'Item B'
+ORDER BY category_id, nullable_date, created_by, status, priority, item_name ASC
+LIMIT 10;
+EXPLAIN
+-> Limit: 10 row(s)  (cost=0.702 rows=2)
+    -> Filter: ((t1.priority = 0) and (t1.`status` = 'Active') and (t1.created_by = 'User1') and (t1.category_id = 100) and (t1.nullable_date is null) and (t1.item_name >= 'Item B'))  (cost=0.702 rows=2)
+        -> Covering index range scan on t1 using idx_covering over (category_id = 100 AND nullable_date = NULL AND created_by = 'User1' AND status = 'Active' AND priority = 0 AND 'Item B' <= item_name)  (cost=0.702 rows=2)
+
+SELECT id, category_id, status, priority, item_name
+FROM t1
+WHERE category_id = 100
+AND nullable_date IS NULL
+AND created_by = 'User1'
+  AND status = 'Active'
+  AND priority = 0
+AND item_name >= 'Item B'
+ORDER BY category_id, nullable_date, created_by, status, priority, item_name ASC
+LIMIT 10;
+id	category_id	status	priority	item_name
+2	100	Active	0	Item B
+3	100	Active	0	Item C
+#
+# Test 3: Mix of equality and IS NULL with all intermediate fields constant
+# All intermediate index fields are constant, so index can provide ordering
+# for item_name without filesort (demonstrates IS NULL works like equality)
+#
+EXPLAIN FORMAT=TREE
+SELECT id, category_id, nullable_date, created_by, status, priority, item_name
+FROM t1 FORCE INDEX(idx_covering)
+WHERE category_id = 100 AND nullable_date IS NULL AND created_by = 'User1' AND status = 'Active' AND priority = 0
+ORDER BY category_id, nullable_date, created_by, status, priority, item_name;
+EXPLAIN
+-> Filter: (t1.nullable_date is null)  (cost=0.35 rows=1)
+    -> Covering index lookup on t1 using idx_covering (category_id = 100, nullable_date = NULL, created_by = 'User1', status = 'Active', priority = 0)  (cost=0.35 rows=1)
+
+#
+# Test 4: IS NOT NULL should NOT be treated as constant
+# This is a negative test - field can have many different non-NULL values
+#
+EXPLAIN FORMAT=TREE
+SELECT id, category_id, nullable_date, item_name
+FROM t1
+WHERE nullable_date IS NOT NULL
+ORDER BY nullable_date, item_name;
+EXPLAIN
+-> Sort: t1.nullable_date, t1.item_name  (cost=0.95 rows=7)
+    -> Filter: (t1.nullable_date is not null)  (cost=0.95 rows=7)
+        -> Covering index scan on t1 using idx_covering  (cost=0.95 rows=7)
+
+#
+# Test 5: Test with optimizer trace to verify "equals_constant_in_where"
+# The trace should show that nullable_date is recognized as constant
+#
+SET optimizer_trace="enabled=on";
+SELECT id, category_id, nullable_date, item_name
+FROM t1 FORCE INDEX(idx_covering)
+WHERE category_id = 100 AND nullable_date IS NULL
+ORDER BY category_id, nullable_date, item_name
+LIMIT 2;
+id	category_id	nullable_date	item_name
+1	100	NULL	Item A
+2	100	NULL	Item B
+SELECT IF(
+LOCATE('"equals_constant_in_where": true', TRACE) > 0,
+'PASS: nullable_date recognized as constant',
+'FAIL: nullable_date not recognized as constant'
+) AS trace_check
+FROM INFORMATION_SCHEMA.OPTIMIZER_TRACE;
+trace_check
+PASS: nullable_date recognized as constant
+SET optimizer_trace="enabled=off";
+#
+# Test 6: OR with IS NULL - field should NOT be treated as constant
+# (nullable_date can be NULL OR have a value, so it's not constant)
+#
+EXPLAIN FORMAT=TREE
+SELECT id, category_id, nullable_date, item_name
+FROM t1
+WHERE category_id = 100 AND (nullable_date IS NULL OR nullable_date > '2024-01-01')
+ORDER BY nullable_date, item_name;
+EXPLAIN
+-> Sort: t1.nullable_date, t1.item_name  (cost=1.43 rows=5)
+    -> Filter: ((t1.category_id = 100) and ((t1.nullable_date is null) or (t1.nullable_date > TIMESTAMP'2024-01-01 00:00:00')))  (cost=1.43 rows=5)
+        -> Covering index range scan on t1 using idx_covering over (category_id = 100 AND nullable_date = NULL) OR (category_id = 100 AND '2024-01-01 00:00:00' < nullable_date)  (cost=1.43 rows=5)
+
+SELECT id, category_id, nullable_date, item_name
+FROM t1
+WHERE category_id = 100 AND (nullable_date IS NULL OR nullable_date > '2024-01-01')
+ORDER BY nullable_date, item_name;
+id	category_id	nullable_date	item_name
+1	100	NULL	Item A
+2	100	NULL	Item B
+3	100	NULL	Item C
+4	100	NULL	Item D
+5	100	2024-01-01 10:00:00	Item E
+#
+# Test 7: OR with multiple IS NULL - same field
+# This is effectively the same as a single IS NULL, so field IS constant
+#
+EXPLAIN FORMAT=TREE
+SELECT id, category_id, nullable_date, item_name
+FROM t1 FORCE INDEX(idx_covering)
+WHERE category_id = 100 AND (nullable_date IS NULL OR nullable_date IS NULL)
+ORDER BY category_id, nullable_date, item_name;
+EXPLAIN
+-> Sort: t1.item_name  (cost=0.775 rows=4)
+    -> Filter: ((t1.nullable_date is null) or (t1.nullable_date is null))  (cost=0.775 rows=4)
+        -> Covering index lookup on t1 using idx_covering (category_id = 100, nullable_date = NULL)  (cost=0.775 rows=4)
+
+#
+# Test 8: Verify IS NULL works with DESC ordering
+# When nullable_date IS NULL with other constants, index can still be used
+# even with DESC on the non-constant field
+#
+EXPLAIN FORMAT=TREE
+SELECT id, category_id, nullable_date, created_by, status, priority, item_name
+FROM t1 FORCE INDEX(idx_covering)
+WHERE category_id = 100 AND nullable_date IS NULL AND created_by = 'User1' AND status = 'Active' AND priority = 0
+ORDER BY category_id, nullable_date, created_by, status, priority, item_name DESC;
+EXPLAIN
+-> Filter: (t1.nullable_date is null)  (cost=0.633 rows=3)
+    -> Covering index lookup on t1 using idx_covering (category_id = 100, nullable_date = NULL, created_by = 'User1', status = 'Active', priority = 0) (reverse)  (cost=0.633 rows=3)
+
+#
+# Test 9: Verify NULL ordering semantics with ASC
+# NULLs should appear FIRST with ORDER BY ASC
+#
+CREATE TABLE t_null_order (
+id INT PRIMARY KEY AUTO_INCREMENT,
+val INT,
+name VARCHAR(10),
+KEY idx_val (val, name)
+);
+INSERT INTO t_null_order (val, name) VALUES
+(NULL, 'null1'),
+(NULL, 'null2'),
+(5, 'five'),
+(10, 'ten'),
+(NULL, 'null3'),
+(1, 'one');
+ANALYZE TABLE t_null_order;
+Table	Op	Msg_type	Msg_text
+test.t_null_order	analyze	status	OK
+SELECT id, val, name FROM t_null_order ORDER BY val ASC, name ASC;
+id	val	name
+1	NULL	null1
+2	NULL	null2
+5	NULL	null3
+6	1	one
+3	5	five
+4	10	ten
+#
+# Test 10: Verify NULL ordering semantics with DESC
+# NULLs should appear LAST with ORDER BY DESC
+#
+SELECT id, val, name FROM t_null_order ORDER BY val DESC, name ASC;
+id	val	name
+4	10	ten
+3	5	five
+6	1	one
+1	NULL	null1
+2	NULL	null2
+5	NULL	null3
+#
+# Test 11: Verify optimization works with DESC and preserves NULL ordering
+# With val IS NULL, val is constant, so should only sort by name
+#
+EXPLAIN FORMAT=TREE
+SELECT id, val, name FROM t_null_order FORCE INDEX(idx_val)
+WHERE val IS NULL
+ORDER BY val DESC, name ASC;
+EXPLAIN
+-> Filter: (t_null_order.val is null)  (cost=0.553 rows=3)
+    -> Covering index lookup on t_null_order using idx_val (val = NULL)  (cost=0.553 rows=3)
+
+SELECT id, val, name FROM t_null_order FORCE INDEX(idx_val)
+WHERE val IS NULL
+ORDER BY val DESC, name ASC;
+id	val	name
+1	NULL	null1
+2	NULL	null2
+5	NULL	null3
+#
+# Test 12: Mixed ASC/DESC with IS NULL constraint
+#
+EXPLAIN FORMAT=TREE
+SELECT id, val, name FROM t_null_order FORCE INDEX(idx_val)
+WHERE val IS NULL
+ORDER BY val ASC, name DESC;
+EXPLAIN
+-> Filter: (t_null_order.val is null)  (cost=0.553 rows=3)
+    -> Covering index lookup on t_null_order using idx_val (val = NULL) (reverse)  (cost=0.553 rows=3)
+
+SELECT id, val, name FROM t_null_order FORCE INDEX(idx_val)
+WHERE val IS NULL
+ORDER BY val ASC, name DESC;
+id	val	name
+5	NULL	null3
+2	NULL	null2
+1	NULL	null1
+DROP TABLE t_null_order;
+DROP TABLE t1;
+#
+# End of test for Bug#119442
+#
diff --git a/mysql-test/r/order_by_none.result b/mysql-test/r/order_by_none.result
@@ -391,7 +391,7 @@ a	b	c
 1	NULL	b
 explain select * from t1 where a = 1 and b is null order by a desc, b desc;
 id	select_type	table	partitions	type	possible_keys	key	key_len	ref	rows	filtered	Extra
-1	SIMPLE	t1	NULL	ref	a	a	9	const,const	2	100.00	Using where; Using index; Using filesort
+1	SIMPLE	t1	NULL	ref	a	a	9	const,const	2	100.00	Using where; Using index
 Warnings:
 Note	1003	/* select#1 */ select `test`.`t1`.`a` AS `a`,`test`.`t1`.`b` AS `b`,`test`.`t1`.`c` AS `c` from `test`.`t1` where ((`test`.`t1`.`a` = 1) and (`test`.`t1`.`b` is null)) order by `test`.`t1`.`a` desc,`test`.`t1`.`b` desc
 select * from t1 where a = 1 and b is null order by a desc, b desc;
@@ -410,7 +410,7 @@ Warnings:
 Note	1003	/* select#1 */ select `test`.`t1`.`a` AS `a`,`test`.`t1`.`b` AS `b`,`test`.`t1`.`c` AS `c` from `test`.`t1` where ((`test`.`t1`.`a` = 2) and (`test`.`t1`.`b` > 0)) order by `test`.`t1`.`a` desc,`test`.`t1`.`b` desc
 explain select * from t1 where a = 2 and b is null order by a desc,b desc;
 id	select_type	table	partitions	type	possible_keys	key	key_len	ref	rows	filtered	Extra
-1	SIMPLE	t1	NULL	ref	a	a	9	const,const	1	100.00	Using where; Using index; Using filesort
+1	SIMPLE	t1	NULL	ref	a	a	9	const,const	1	100.00	Using where; Using index
 Warnings:
 Note	1003	/* select#1 */ select `test`.`t1`.`a` AS `a`,`test`.`t1`.`b` AS `b`,`test`.`t1`.`c` AS `c` from `test`.`t1` where ((`test`.`t1`.`a` = 2) and (`test`.`t1`.`b` is null)) order by `test`.`t1`.`a` desc,`test`.`t1`.`b` desc
 explain select * from t1 where a = 2 and (b is null or b > 0) order by a