MariaDB · DaveGosselin-MariaDB · May 6, 2026
diff --git a/mysql-test/main/derived_view.result b/mysql-test/main/derived_view.result
@@ -4430,3 +4430,97 @@ deallocate prepare stmt;
 drop view v1,v2;
 drop table t1,t2;
 # End of 10.6 tests
+#
+# Beginning of 10.11 tests
+#
+#
+# MDEV-37020: derived table not merged in multi-table DELETE/UPDATE
+#             while equivalent SELECT and view-based form do merge
+#
+create table t1 (a int, b int);
+insert into t1 select seq, seq from seq_1_to_10;
+create table t2 (a int, b int);
+insert into t2 select seq, seq from seq_1_to_10;
+create table t3 (a int, b int);
+insert into t3 select seq, seq from seq_1_to_10;
+# Baseline: equivalent SELECT merges the derived table.
+explain select * from t1, (select t2.b as b1 from t2, t3 where t3.a=t2.a and t2.a<5) dt
+where t1.b+1=1+dt.b1;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t1	ALL	NULL	NULL	NULL	NULL	10	
+1	SIMPLE	t2	ALL	NULL	NULL	NULL	NULL	10	Using where; Using join buffer (flat, BNL join)
+1	SIMPLE	t3	ALL	NULL	NULL	NULL	NULL	10	Using where; Using join buffer (incremental, BNL join)
+# Multitable DELETE must merge the derived table.
+explain delete t1.* from t1, (select t2.b as b1 from t2, t3 where t3.a=t2.a) dt
+where t1.b+1=1+dt.b1;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t1	ALL	NULL	NULL	NULL	NULL	10	
+1	SIMPLE	t2	ALL	NULL	NULL	NULL	NULL	10	Using where
+1	SIMPLE	t3	ALL	NULL	NULL	NULL	NULL	10	Using where
+# Multitable UPDATE must merge the derived table.
+explain update t1, (select t2.b as b1 from t2, t3 where t3.a=t2.a) dt
+set t1.a=t1.a+1 where t1.b+1=1+dt.b1;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t1	ALL	NULL	NULL	NULL	NULL	10	
+1	SIMPLE	t2	ALL	NULL	NULL	NULL	NULL	10	Using where
+1	SIMPLE	t3	ALL	NULL	NULL	NULL	NULL	10	Using where
+# VIEW form already merged the derived table before this fix, verify.
+create view v1 as select t2.b as b1 from t2, t3 where t3.a=t2.a;
+select t1.* from t1, v1 where t1.b+1=1+v1.b1;
+a	b
+1	1
+2	2
+3	3
+4	4
+5	5
+6	6
+7	7
+8	8
+9	9
+10	10
+explain select t1.* from t1, v1 where t1.b+1=1+v1.b1;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t1	ALL	NULL	NULL	NULL	NULL	10	
+1	SIMPLE	t2	ALL	NULL	NULL	NULL	NULL	10	Using where; Using join buffer (flat, BNL join)
+1	SIMPLE	t3	ALL	NULL	NULL	NULL	NULL	10	Using where; Using join buffer (incremental, BNL join)
+explain delete t1.* from t1, v1 where t1.b+1=1+v1.b1;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t1	ALL	NULL	NULL	NULL	NULL	10	
+1	SIMPLE	t2	ALL	NULL	NULL	NULL	NULL	10	Using where
+1	SIMPLE	t3	ALL	NULL	NULL	NULL	NULL	10	Using where
+explain update t1, v1 set t1.a=t1.a+1 where t1.b+1=1+v1.b1;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t1	ALL	NULL	NULL	NULL	NULL	10	
+1	SIMPLE	t2	ALL	NULL	NULL	NULL	NULL	10	Using where
+1	SIMPLE	t3	ALL	NULL	NULL	NULL	NULL	10	Using where
+# Confirm queries still produce the correct results.
+select t1.* from t1, (select t2.b as b1 from t2, t3 where t3.a=t2.a and t2.a<5) dt
+where t1.b+1=1+dt.b1;
+a	b
+1	1
+2	2
+3	3
+4	4
+delete t1.* from t1, (select t2.b as b1 from t2, t3 where t3.a=t2.a and t2.a<5) dt2
+where t1.b=dt2.b1;
+select * from t1 order by a;
+a	b
+5	5
+6	6
+7	7
+8	8
+9	9
+10	10
+update t1, (select t2.b as b1 from t2, t3 where t3.a=t2.a and t2.a>7) dt2
+set t1.a=t1.a*100 where t1.b=dt2.b1;
+select * from t1 order by b;
+a	b
+5	5
+6	6
+7	7
+800	8
+900	9
+1000	10
+drop view v1;
+drop table t1, t2, t3;
+# End of 10.11 tests
diff --git a/mysql-test/main/derived_view.test b/mysql-test/main/derived_view.test
@@ -2940,3 +2940,54 @@ drop view v1,v2;
 drop table t1,t2;
 
 --echo # End of 10.6 tests
+
+
+--echo #
+--echo # Beginning of 10.11 tests
+--echo #
+
+--echo #
+--echo # MDEV-37020: derived table not merged in multi-table DELETE/UPDATE
+--echo #             while equivalent SELECT and view-based form do merge
+--echo #
+
+create table t1 (a int, b int);
+insert into t1 select seq, seq from seq_1_to_10;
+create table t2 (a int, b int);
+insert into t2 select seq, seq from seq_1_to_10;
+create table t3 (a int, b int);
+insert into t3 select seq, seq from seq_1_to_10;
+
+--echo # Baseline: equivalent SELECT merges the derived table.
+explain select * from t1, (select t2.b as b1 from t2, t3 where t3.a=t2.a and t2.a<5) dt
+  where t1.b+1=1+dt.b1;
+
+--echo # Multitable DELETE must merge the derived table.
+explain delete t1.* from t1, (select t2.b as b1 from t2, t3 where t3.a=t2.a) dt
+  where t1.b+1=1+dt.b1;
+
+--echo # Multitable UPDATE must merge the derived table.
+explain update t1, (select t2.b as b1 from t2, t3 where t3.a=t2.a) dt
+  set t1.a=t1.a+1 where t1.b+1=1+dt.b1;
+
+--echo # VIEW form already merged the derived table before this fix, verify.
+create view v1 as select t2.b as b1 from t2, t3 where t3.a=t2.a;
+select t1.* from t1, v1 where t1.b+1=1+v1.b1;
+explain select t1.* from t1, v1 where t1.b+1=1+v1.b1;
+explain delete t1.* from t1, v1 where t1.b+1=1+v1.b1;
+explain update t1, v1 set t1.a=t1.a+1 where t1.b+1=1+v1.b1;
+
+--echo # Confirm queries still produce the correct results.
+select t1.* from t1, (select t2.b as b1 from t2, t3 where t3.a=t2.a and t2.a<5) dt
+  where t1.b+1=1+dt.b1;
+delete t1.* from t1, (select t2.b as b1 from t2, t3 where t3.a=t2.a and t2.a<5) dt2
+  where t1.b=dt2.b1;
+select * from t1 order by a;
+update t1, (select t2.b as b1 from t2, t3 where t3.a=t2.a and t2.a>7) dt2
+  set t1.a=t1.a*100 where t1.b=dt2.b1;
+select * from t1 order by b;
+
+drop view v1;
+drop table t1, t2, t3;
+
+--echo # End of 10.11 tests
diff --git a/mysql-test/main/multi_update.result b/mysql-test/main/multi_update.result
@@ -585,9 +585,6 @@ INSERT INTO t3 VALUES (1), (2);
 UPDATE IGNORE
 ( SELECT ( SELECT COUNT(*) FROM t1 GROUP BY a, @v ) a FROM t2 ) x, t3
 SET t3.a = 0;
-Warnings:
-Warning	1242	Subquery returns more than 1 row
-Warning	1242	Subquery returns more than 1 row
 DROP TABLE t1, t2, t3;
 SET SESSION sql_safe_updates = DEFAULT;
 #

diff --git a/mysql-test/main/myisam_explain_non_select_all.result b/mysql-test/main/myisam_explain_non_select_all.result
@@ -198,18 +198,16 @@ Warnings:
 Warning	1287	'<select expression> INTO <destination>;' is deprecated and will be removed in a future release. Please use 'SELECT <select list> INTO <destination> FROM...' instead
 EXPLAIN UPDATE        t1 t11, (SELECT * FROM t2) t12 SET t11.a = 10 WHERE t11.a = 1;
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
-1	PRIMARY	t11	ALL	NULL	NULL	NULL	NULL	3	Using where
-1	PRIMARY	<derived2>	ALL	NULL	NULL	NULL	NULL	3	
-2	DERIVED	t2	ALL	NULL	NULL	NULL	NULL	3	
+1	SIMPLE	t11	ALL	NULL	NULL	NULL	NULL	3	Using where
+1	SIMPLE	t2	ALL	NULL	NULL	NULL	NULL	3	
 FLUSH STATUS;
 FLUSH TABLES;
 EXPLAIN EXTENDED UPDATE        t1 t11, (SELECT * FROM t2) t12 SET t11.a = 10 WHERE t11.a = 1;
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
-1	PRIMARY	t11	ALL	NULL	NULL	NULL	NULL	3	100.00	Using where
-1	PRIMARY	<derived2>	ALL	NULL	NULL	NULL	NULL	3	100.00	
-2	DERIVED	t2	ALL	NULL	NULL	NULL	NULL	3	100.00	
+1	SIMPLE	t11	ALL	NULL	NULL	NULL	NULL	3	100.00	Using where
+1	SIMPLE	t2	ALL	NULL	NULL	NULL	NULL	3	100.00	
 Warnings:
-Note	1003	/* select#1 */ update `test`.`t1` `t11` join (/* select#2 */ select `test`.`t2`.`b` AS `b` from `test`.`t2`) `t12` set `test`.`t11`.`a` = 10 where `test`.`t11`.`a` = 1
+Note	1003	update `test`.`t1` `t11` join `test`.`t2` set `test`.`t11`.`a` = 10 where `test`.`t11`.`a` = 1
 # Status of EXPLAIN EXTENDED query
 Variable_name	Value
 Handler_read_key	4
@@ -233,7 +231,7 @@ Handler_read_rnd_next	8
 # Status of testing query execution:
 Variable_name	Value
 Handler_read_key	4
-Handler_read_rnd_next	12
+Handler_read_rnd_next	8
 Handler_update	1
 
 DROP TABLE t1, t2;
@@ -410,18 +408,16 @@ Warnings:
 Warning	1287	'<select expression> INTO <destination>;' is deprecated and will be removed in a future release. Please use 'SELECT <select list> INTO <destination> FROM...' instead
 EXPLAIN UPDATE        t1 t11, (SELECT * FROM t2) t12 SET t11.a = t11.a + 10;
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
-1	PRIMARY	t11	ALL	NULL	NULL	NULL	NULL	3	
-1	PRIMARY	<derived2>	ALL	NULL	NULL	NULL	NULL	3	
-2	DERIVED	t2	ALL	NULL	NULL	NULL	NULL	3	
+1	SIMPLE	t11	ALL	NULL	NULL	NULL	NULL	3	
+1	SIMPLE	t2	ALL	NULL	NULL	NULL	NULL	3	
 FLUSH STATUS;
 FLUSH TABLES;
 EXPLAIN EXTENDED UPDATE        t1 t11, (SELECT * FROM t2) t12 SET t11.a = t11.a + 10;
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
-1	PRIMARY	t11	ALL	NULL	NULL	NULL	NULL	3	100.00	
-1	PRIMARY	<derived2>	ALL	NULL	NULL	NULL	NULL	3	100.00	
-2	DERIVED	t2	ALL	NULL	NULL	NULL	NULL	3	100.00	
+1	SIMPLE	t11	ALL	NULL	NULL	NULL	NULL	3	100.00	
+1	SIMPLE	t2	ALL	NULL	NULL	NULL	NULL	3	100.00	
 Warnings:
-Note	1003	/* select#1 */ update `test`.`t1` `t11` join (/* select#2 */ select `test`.`t2`.`b` AS `b` from `test`.`t2`) `t12` set `test`.`t11`.`a` = `test`.`t11`.`a` + 10
+Note	1003	update `test`.`t1` `t11` join `test`.`t2` set `test`.`t11`.`a` = `test`.`t11`.`a` + 10
 # Status of EXPLAIN EXTENDED query
 Variable_name	Value
 Handler_read_key	4
@@ -447,7 +443,7 @@ Variable_name	Value
 Handler_read_key	4
 Handler_read_rnd	3
 Handler_read_rnd_deleted	1
-Handler_read_rnd_next	24
+Handler_read_rnd_next	20
 Handler_update	3
 
 DROP TABLE t1, t2;
@@ -520,18 +516,16 @@ Warnings:
 Warning	1287	'<select expression> INTO <destination>;' is deprecated and will be removed in a future release. Please use 'SELECT <select list> INTO <destination> FROM...' instead
 EXPLAIN UPDATE        t1 t11, (SELECT * FROM t2) t12 SET t11.a = 10 WHERE t11.a > 1;
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
-1	PRIMARY	t11	ALL	NULL	NULL	NULL	NULL	3	Using where
-1	PRIMARY	<derived2>	ALL	NULL	NULL	NULL	NULL	3	
-2	DERIVED	t2	ALL	NULL	NULL	NULL	NULL	3	
+1	SIMPLE	t11	ALL	NULL	NULL	NULL	NULL	3	Using where
+1	SIMPLE	t2	ALL	NULL	NULL	NULL	NULL	3	
 FLUSH STATUS;
 FLUSH TABLES;
 EXPLAIN EXTENDED UPDATE        t1 t11, (SELECT * FROM t2) t12 SET t11.a = 10 WHERE t11.a > 1;
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
-1	PRIMARY	t11	ALL	NULL	NULL	NULL	NULL	3	100.00	Using where
-1	PRIMARY	<derived2>	ALL	NULL	NULL	NULL	NULL	3	100.00	
-2	DERIVED	t2	ALL	NULL	NULL	NULL	NULL	3	100.00	
+1	SIMPLE	t11	ALL	NULL	NULL	NULL	NULL	3	100.00	Using where
+1	SIMPLE	t2	ALL	NULL	NULL	NULL	NULL	3	100.00	
 Warnings:
-Note	1003	/* select#1 */ update `test`.`t1` `t11` join (/* select#2 */ select `test`.`t2`.`b` AS `b` from `test`.`t2`) `t12` set `test`.`t11`.`a` = 10 where `test`.`t11`.`a` > 1
+Note	1003	update `test`.`t1` `t11` join `test`.`t2` set `test`.`t11`.`a` = 10 where `test`.`t11`.`a` > 1
 # Status of EXPLAIN EXTENDED query
 Variable_name	Value
 Handler_read_key	4
@@ -555,7 +549,7 @@ Handler_read_rnd_next	8
 # Status of testing query execution:
 Variable_name	Value
 Handler_read_key	4
-Handler_read_rnd_next	16
+Handler_read_rnd_next	12
 Handler_update	2
 
 DROP TABLE t1, t2;
@@ -3409,20 +3403,18 @@ EXPLAIN UPDATE        t1, (SELECT * FROM t2) y SET a = 10 WHERE a IN (SELECT * F
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	3	Using where
 1	PRIMARY	<derived4>	ref	key0	key0	5	test.t1.a	2	FirstMatch(t1)
-1	PRIMARY	<derived2>	ALL	NULL	NULL	NULL	NULL	3	
+1	PRIMARY	t2	ALL	NULL	NULL	NULL	NULL	3	
 4	DERIVED	t2	ALL	NULL	NULL	NULL	NULL	3	Using filesort
-2	DERIVED	t2	ALL	NULL	NULL	NULL	NULL	3	
 FLUSH STATUS;
 FLUSH TABLES;
 EXPLAIN EXTENDED UPDATE        t1, (SELECT * FROM t2) y SET a = 10 WHERE a IN (SELECT * FROM (SELECT b FROM t2 ORDER BY b LIMIT 2,2) x);
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
 1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	3	100.00	Using where
 1	PRIMARY	<derived4>	ref	key0	key0	5	test.t1.a	2	100.00	FirstMatch(t1)
-1	PRIMARY	<derived2>	ALL	NULL	NULL	NULL	NULL	3	100.00	
+1	PRIMARY	t2	ALL	NULL	NULL	NULL	NULL	3	100.00	
 4	DERIVED	t2	ALL	NULL	NULL	NULL	NULL	3	100.00	Using filesort
-2	DERIVED	t2	ALL	NULL	NULL	NULL	NULL	3	100.00	
 Warnings:
-Note	1003	/* select#1 */ update `test`.`t1` semi join ((/* select#4 */ select `test`.`t2`.`b` AS `b` from `test`.`t2` order by `test`.`t2`.`b` limit 2,2) `x`) join (/* select#2 */ select `test`.`t2`.`b` AS `b` from `test`.`t2`) `y` set `test`.`t1`.`a` = 10 where `x`.`b` = `test`.`t1`.`a`
+Note	1003	/* select#1 */ update `test`.`t1` semi join ((/* select#4 */ select `test`.`t2`.`b` AS `b` from `test`.`t2` order by `test`.`t2`.`b` limit 2,2) `x`) join `test`.`t2` set `test`.`t1`.`a` = 10 where `x`.`b` = `test`.`t1`.`a`
 # Status of EXPLAIN EXTENDED query
 Variable_name	Value
 Handler_read_key	4

diff --git a/sql/sql_update.cc b/sql/sql_update.cc
@@ -1733,6 +1733,19 @@ static bool multi_update_check_table_access(THD *thd, TABLE_LIST *table,
   }
   else
   {
+    /*
+      A merged derived table that is not a VIEW has no TABLE* so we
+      can't check privileges on it here.  Besides, the privileges for
+      the underlying base tables are already checked by
+      multi_update_precheck.
+
+      Without this guard, the main.lock_multi_bug38499 test will crash
+      just below when running a prepared statement that is made from an
+      UPDATE.
+    */
+    if (table->is_merged_derived())
+      return false;
+
     /* Must be a base or derived table. */
     const bool updated= table->table->map & tables_for_update;
     if (check_table_access(thd, updated ? UPDATE_ACL : SELECT_ACL, table,

diff --git a/sql/table.cc b/sql/table.cc
@@ -9903,8 +9903,14 @@ bool TABLE_LIST::init_derived(THD *thd, bool init_view)
         (is_view() ||
          optimizer_flag(thd, OPTIMIZER_SWITCH_DERIVED_MERGE)) &&
           !thd->lex->can_not_use_merged() &&
+        /*
+          Allow merged derived optimization for multitable DELETE and
+          UPDATE, but with one exception: if this derived table is
+          itself within a VIEW, then don't allow it to be merged.
+        */
         !((thd->lex->sql_command == SQLCOM_UPDATE_MULTI ||
-           thd->lex->sql_command == SQLCOM_DELETE_MULTI) && !is_view()) &&
+           thd->lex->sql_command == SQLCOM_DELETE_MULTI) &&
+          !is_view() && belong_to_view) &&
         !is_recursive_with_table())
       set_merged_derived();
     else