MDEV-30538 Plans for SELECT and multi-table UPDATE/DELETE unexpectedly differ

This patch allowed transformation of EXISTS subqueries into equivalent
IN predicands at the top level of WHERE conditions for multi-table UPDATE
and DELETE statements. There was no reason to prohibit the transformation
for such statements. The transformation provides more opportunities of
using semi-join optimizations.

Approved by Oleksandr Byelkin <sanja@mariadb.com>

4 files changed, 201 insertions, 5 deletions

diff --git a/mysql-test/main/multi_update.result b/mysql-test/main/multi_update.result
index 61e04c3d4a9..d6cf9ba685f 100644
--- a/mysql-test/main/multi_update.result
+++ b/mysql-test/main/multi_update.result
@@ -1251,3 +1251,123 @@ EXPLAIN
   }
 }
 DROP TABLES t1, t2;
+# End of 10.3 tests
+#
+# MDEV-28538: multi-table UPDATE/DELETE with possible exists-to-in
+#
+create table t1 (c1 int, c2 int, c3 int, index idx(c2));
+insert into t1 values
+(1,1,1),(3,2,2),(1,3,3),
+(2,1,4),(2,2,5),(4,3,6),
+(2,4,7),(2,5,8);
+create table t2 (c1 int, c2 int, c3 int, index idx(c2));
+insert into t2 values
+(1,7,1),(1,8,2),(1,3,3),
+(2,1,4),(2,2,5),(2,3,6),
+(2,4,7),(2,5,8);
+create table t3 (c1 int, c2 int, c3 int, index idx(c2));
+insert into t3 values
+(1,1,1),(1,2,2),(1,3,3),
+(2,1,4),(2,2,5),(2,3,6),
+(2,4,7),(2,5,8);
+insert into t3 select c1+1, c2+2, c3 from t3;
+insert into t3 select c1, c2+2, c3  from t3;
+analyze table t1,t2,t3 persistent for all;
+Table	Op	Msg_type	Msg_text
+test.t1	analyze	status	Engine-independent statistics collected
+test.t1	analyze	status	OK
+test.t2	analyze	status	Engine-independent statistics collected
+test.t2	analyze	status	OK
+test.t3	analyze	status	Engine-independent statistics collected
+test.t3	analyze	status	OK
+explain select * from t1,t3
+where t1.c2 = t3.c2 and
+t1.c1 > 1 and
+exists (select 'X' from t2 where t2.c1 = t1.c1 and t2.c2 > 4);
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	ALL	idx	NULL	NULL	NULL	8	Using where
+1	PRIMARY	<subquery2>	eq_ref	distinct_key	distinct_key	4	func	1	
+1	PRIMARY	t3	ref	idx	idx	5	test.t1.c2	3	
+2	MATERIALIZED	t2	range	idx	idx	5	NULL	3	Using index condition; Using where
+explain delete from t1 using t1,t3
+where t1.c2 = t3.c2 and
+t1.c1 > 1 and
+exists (select 'X' from t2 where t2.c1 = t1.c1 and t2.c2 > 4);
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	ALL	idx	NULL	NULL	NULL	8	Using where
+1	PRIMARY	<subquery2>	eq_ref	distinct_key	distinct_key	4	func	1	
+1	PRIMARY	t3	ref	idx	idx	5	test.t1.c2	3	Using index
+2	MATERIALIZED	t2	range	idx	idx	5	NULL	3	Using where
+explain update t1,t3 set t1.c1 = t1.c1+10
+where t1.c2 = t3.c2 and
+t1.c1 > 1 and
+exists (select 'X' from t2 where t2.c1 = t1.c1 and t2.c2 > 4);
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	ALL	idx	NULL	NULL	NULL	8	Using where
+1	PRIMARY	<subquery2>	eq_ref	distinct_key	distinct_key	4	func	1	
+1	PRIMARY	t3	ref	idx	idx	5	test.t1.c2	3	Using index
+2	MATERIALIZED	t2	range	idx	idx	5	NULL	3	Using where
+create table t as select * from t1;
+select * from t1,t3
+where t1.c2 = t3.c2 and
+t1.c1 > 1 and
+exists (select 'X' from t2 where t2.c1 = t1.c1 and t2.c2 > 4);
+c1	c2	c3	c1	c2	c3
+2	1	4	1	1	1
+2	1	4	2	1	4
+2	2	5	1	2	2
+2	2	5	2	2	5
+2	4	7	2	4	7
+2	4	7	2	4	2
+2	4	7	3	4	5
+2	4	7	1	4	2
+2	4	7	2	4	5
+2	5	8	2	5	8
+2	5	8	2	5	3
+2	5	8	3	5	6
+2	5	8	1	5	3
+2	5	8	2	5	6
+2	5	8	2	5	1
+2	5	8	3	5	4
+select * from t1;
+c1	c2	c3
+1	1	1
+3	2	2
+1	3	3
+2	1	4
+2	2	5
+4	3	6
+2	4	7
+2	5	8
+delete from t1 using t1,t3
+where t1.c2 = t3.c2 and
+t1.c1 > 1 and
+exists (select 'X' from t2 where t2.c1 = t1.c1 and t2.c2 > 4);
+select * from t1;
+c1	c2	c3
+1	1	1
+3	2	2
+1	3	3
+4	3	6
+truncate table t1;
+insert into t1 select * from t;
+analyze table t1 persistent for all;
+Table	Op	Msg_type	Msg_text
+test.t1	analyze	status	Engine-independent statistics collected
+test.t1	analyze	status	Table is already up to date
+update t1,t3 set t1.c1 = t1.c1+10
+where t1.c2 = t3.c2 and
+t1.c1 > 1 and
+exists (select 'X' from t2 where t2.c1 = t1.c1 and t2.c2 > 4);
+select * from t1;
+c1	c2	c3
+1	1	1
+3	2	2
+1	3	3
+12	1	4
+12	2	5
+4	3	6
+12	4	7
+12	5	8
+drop table t1,t2,t3,t;
+# End of 10.4 tests
diff --git a/mysql-test/main/multi_update.test b/mysql-test/main/multi_update.test
index 54c64918e03..48e6250393b 100644
--- a/mysql-test/main/multi_update.test
+++ b/mysql-test/main/multi_update.test
@@ -1130,3 +1130,73 @@ EXPLAIN FORMAT=JSON UPDATE t2 JOIN t1 USING(a) SET t2.part=2 WHERE t2.part=1 AND
 EXPLAIN FORMAT=JSON UPDATE t2 JOIN t1 USING(a) SET t2.part=3 WHERE t2.part=2 AND t1.part=2;
 
 DROP TABLES t1, t2;
+
+--echo # End of 10.3 tests
+
+--echo #
+--echo # MDEV-28538: multi-table UPDATE/DELETE with possible exists-to-in
+--echo #
+
+create table t1 (c1 int, c2 int, c3 int, index idx(c2));
+insert into t1 values
+(1,1,1),(3,2,2),(1,3,3),
+(2,1,4),(2,2,5),(4,3,6),
+(2,4,7),(2,5,8);
+
+create table t2 (c1 int, c2 int, c3 int, index idx(c2));
+insert into t2 values
+(1,7,1),(1,8,2),(1,3,3),
+(2,1,4),(2,2,5),(2,3,6),
+(2,4,7),(2,5,8);
+
+create table t3 (c1 int, c2 int, c3 int, index idx(c2));
+insert into t3 values
+(1,1,1),(1,2,2),(1,3,3),
+(2,1,4),(2,2,5),(2,3,6),
+(2,4,7),(2,5,8);
+insert into t3 select c1+1, c2+2, c3 from t3;
+insert into t3 select c1, c2+2, c3  from t3;
+
+analyze table t1,t2,t3 persistent for all;
+
+let $c=
+  t1.c2 = t3.c2 and
+  t1.c1 > 1 and
+  exists (select 'X' from t2 where t2.c1 = t1.c1 and t2.c2 > 4);
+
+let $q1=
+select * from t1,t3
+where $c;
+
+eval explain $q1;
+
+let $q2=
+delete from t1 using t1,t3
+where $c;
+
+eval explain $q2;
+
+let $q3=
+update t1,t3 set t1.c1 = t1.c1+10
+where $c;
+
+eval explain $q3;
+
+create table t as select * from t1;
+
+eval $q1;
+select * from t1;
+
+eval $q2;
+select * from t1;
+
+truncate table t1;
+insert into t1 select * from t;
+analyze table t1 persistent for all;
+
+eval $q3;
+select * from t1;
+
+drop table t1,t2,t3,t;
+
+--echo # End of 10.4 tests
diff --git a/mysql-test/main/update_use_source.result b/mysql-test/main/update_use_source.result
index 9e43b54d81c..57787671e77 100644
--- a/mysql-test/main/update_use_source.result
+++ b/mysql-test/main/update_use_source.result
@@ -76,7 +76,8 @@ rollback;
 explain update t1 set c1=0 where exists (select 'X' from t1 a where a.c2 = t1.c2) and c2 > 3;
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	8	Using where
-2	DEPENDENT SUBQUERY	a	ALL	NULL	NULL	NULL	NULL	8	Using where
+1	PRIMARY	<subquery2>	eq_ref	distinct_key	distinct_key	4	func	1	
+2	MATERIALIZED	a	ALL	NULL	NULL	NULL	NULL	8	
 start transaction;
 update t1 set c1=c1+10 where exists (select 'X' from t1 a where a.c2 = t1.c2) and c2 >= 3;
 affected rows: 4
@@ -317,7 +318,8 @@ rollback;
 explain update t1 set c1=0 where exists (select 'X' from t1 a where a.c2 = t1.c2) and c2 > 3;
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	PRIMARY	t1	range	t1_c2	t1_c2	5	NULL	2	Using where
-2	DEPENDENT SUBQUERY	a	ref	t1_c2	t1_c2	5	test.t1.c2	4	Using index
+1	PRIMARY	<subquery2>	eq_ref	distinct_key	distinct_key	4	func	1	
+2	MATERIALIZED	a	range	t1_c2	t1_c2	5	NULL	2	Using where; Using index
 start transaction;
 update t1 set c1=c1+10 where exists (select 'X' from t1 a where a.c2 = t1.c2) and c2 >= 3;
 affected rows: 4
@@ -558,7 +560,8 @@ rollback;
 explain update t1 set c1=0 where exists (select 'X' from t1 a where a.c2 = t1.c2) and c2 > 3;
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	PRIMARY	t1	range	t1_c2	t1_c2	5	NULL	2	Using where
-2	DEPENDENT SUBQUERY	a	ref	t1_c2	t1_c2	5	test.t1.c2	1	Using index
+1	PRIMARY	<subquery2>	eq_ref	distinct_key	distinct_key	4	func	1	
+2	MATERIALIZED	a	range	t1_c2	t1_c2	5	NULL	2	Using where; Using index
 start transaction;
 update t1 set c1=c1+10 where exists (select 'X' from t1 a where a.c2 = t1.c2) and c2 >= 3;
 affected rows: 4
@@ -800,7 +803,8 @@ rollback;
 explain update t1 set c1=0 where exists (select 'X' from t1 a where a.c2 = t1.c2) and c2 > 3;
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	PRIMARY	t1	range	t1_c2	t1_c2	5	NULL	2	Using where
-2	DEPENDENT SUBQUERY	a	ref	t1_c2	t1_c2	5	test.t1.c2	1	Using index
+1	PRIMARY	<subquery2>	eq_ref	distinct_key	distinct_key	4	func	1	
+2	MATERIALIZED	a	range	t1_c2	t1_c2	5	NULL	2	Using where; Using index
 start transaction;
 update t1 set c1=c1+10 where exists (select 'X' from t1 a where a.c2 = t1.c2) and c2 >= 3;
 affected rows: 4
diff --git a/sql/item_subselect.cc b/sql/item_subselect.cc
index 461bd9fb144..1454073e459 100644
--- a/sql/item_subselect.cc
+++ b/sql/item_subselect.cc
@@ -2825,7 +2825,9 @@ bool Item_exists_subselect::select_prepare_to_be_in()
   bool trans_res= FALSE;
   DBUG_ENTER("Item_exists_subselect::select_prepare_to_be_in");
   if (!optimizer &&
-      thd->lex->sql_command == SQLCOM_SELECT &&
+      (thd->lex->sql_command == SQLCOM_SELECT ||
+       thd->lex->sql_command == SQLCOM_UPDATE_MULTI ||
+       thd->lex->sql_command == SQLCOM_DELETE_MULTI) &&
       !unit->first_select()->is_part_of_union() &&
       optimizer_flag(thd, OPTIMIZER_SWITCH_EXISTS_TO_IN) &&
       (is_top_level_item() ||