Bug#20729351 ASSERTION FAILED: ITEM_IN->LEFT_EXPR->ELEMENT_INDEX(0)->MAYBE_NULL

A recently added assertion fails.
(SELECT NULL IN (NULL) FROM t1 WHERE a) =ANY(SELECT 1 FROM t2):
=ANY is identical to IN and is processed with subquery
materialization. The left argument is Item_cache wrapping
"NULL=NULL"; that equality item has maybe_null=true but
the wrapping Item_cache has maybe_null=false, which is
inconsistent and causes the problem.
Actually, Item_cache starts with null_value=true, so it
looks logical to set maybe_null to true unconditionally.
An alternative fix would be to:
- assume that this initial null_value is never returned
(i.e. we never cal val*() before having cached a value)
- start with maybe_null=false
- set maybe_null=example->maybe_null in setup()
- but store() changes "example" and it's too late to change
the item_cache's maybe_null at this point.
So setting unconditionally looks like the safest choice.
About result change in "Note": it is due to nullability.

Author: Guilhem Bichot

mysql-test/include/subquery_mat.inc

@@ -1577,5 +1577,20 @@ eval $query;
 
 DROP TABLE t1,t2;
 
+--echo #
+--echo # Bug#20729351 ASSERTION FAILED: ITEM_IN->LEFT_EXPR->ELEMENT_INDEX(0)->MAYBE_NULL
+--echo #
+
+CREATE TABLE t1 (a LONGBLOB) ENGINE=INNODB;
+INSERT INTO t1 VALUES ('a'), ('a'), ('a');
+CREATE TABLE t2 (a INT) ENGINE=INNODB;
+INSERT INTO t2 VALUES(1), (1), (1), (1);
+ANALYZE TABLE t1, t2;
+SELECT
+ (SELECT NULL IN (NULL) FROM t1 WHERE a) =
+  ANY(SELECT 1 FROM t2)
+FROM t1;
+DROP TABLE t1, t2;
+
 set @@optimizer_switch=@old_opt_switch;
 SET sql_mode = default;

mysql-test/r/subquery_mat.result

@@ -2159,11 +2159,32 @@ id	select_type	table	partitions	type	possible_keys	key	key_len	ref	rows	filtered
 3	DEPENDENT SUBQUERY	t1	NULL	ALL	NULL	NULL	NULL	NULL	1	100.00	NULL
 2	SUBQUERY	t2	NULL	ALL	NULL	NULL	NULL	NULL	1	100.00	NULL
 Warnings:
-Note	1003	/* select#1 */ select (not(<in_optimizer>((/* select#2 */ select 1,2 from `test`.`t2`),<exists>(/* select#3 */ select 1,1 from `test`.`t1` where 1 having 1)))) AS `(SELECT 1,2 FROM t2) NOT IN (SELECT 1,2 FROM t1)` from `test`.`t1`
+Note	1003	/* select#1 */ select (not(<in_optimizer>((/* select#2 */ select 1,2 from `test`.`t2`),<exists>(/* select#3 */ select 1,1 from `test`.`t1` where (<if>(outer_field_is_not_null, ((<cache>(<cache>(1)) = 1) or isnull(1)), true) and <if>(outer_field_is_not_null, ((<cache>(<cache>(2)) = 2) or isnull(2)), true)) having (<if>(outer_field_is_not_null, <cache>(<is_not_null_test>(1)), true) and <if>(outer_field_is_not_null, <cache>(<is_not_null_test>(2)), true)))))) AS `(SELECT 1,2 FROM t2) NOT IN (SELECT 1,2 FROM t1)` from `test`.`t1`
 SELECT (SELECT 1,2 FROM t2) NOT IN (SELECT 1,2 FROM t1) FROM t1;
 (SELECT 1,2 FROM t2) NOT IN (SELECT 1,2 FROM t1)
 NULL
 DROP TABLE t1,t2;
+#
+# Bug#20729351 ASSERTION FAILED: ITEM_IN->LEFT_EXPR->ELEMENT_INDEX(0)->MAYBE_NULL
+#
+CREATE TABLE t1 (a LONGBLOB) ENGINE=INNODB;
+INSERT INTO t1 VALUES ('a'), ('a'), ('a');
+CREATE TABLE t2 (a INT) ENGINE=INNODB;
+INSERT INTO t2 VALUES(1), (1), (1), (1);
+ANALYZE TABLE t1, t2;
+Table	Op	Msg_type	Msg_text
+test.t1	analyze	status	OK
+test.t2	analyze	status	OK
+SELECT
+(SELECT NULL IN (NULL) FROM t1 WHERE a) =
+ANY(SELECT 1 FROM t2)
+FROM t1;
+(SELECT NULL IN (NULL) FROM t1 WHERE a) =
+ANY(SELECT 1 FROM t2)
+NULL
+NULL
+NULL
+DROP TABLE t1, t2;
 set @@optimizer_switch=@old_opt_switch;
 SET sql_mode = default;
 set global innodb_large_prefix=default;

mysql-test/r/subquery_mat_all.result

@@ -2160,11 +2160,32 @@ id	select_type	table	partitions	type	possible_keys	key	key_len	ref	rows	filtered
 3	DEPENDENT SUBQUERY	t1	NULL	ALL	NULL	NULL	NULL	NULL	1	100.00	NULL
 2	SUBQUERY	t2	NULL	ALL	NULL	NULL	NULL	NULL	1	100.00	NULL
 Warnings:
-Note	1003	/* select#1 */ select (not(<in_optimizer>((/* select#2 */ select 1,2 from `test`.`t2`),<exists>(/* select#3 */ select 1,1 from `test`.`t1` where 1 having 1)))) AS `(SELECT 1,2 FROM t2) NOT IN (SELECT 1,2 FROM t1)` from `test`.`t1`
+Note	1003	/* select#1 */ select (not(<in_optimizer>((/* select#2 */ select 1,2 from `test`.`t2`),<exists>(/* select#3 */ select 1,1 from `test`.`t1` where (<if>(outer_field_is_not_null, ((<cache>(<cache>(1)) = 1) or isnull(1)), true) and <if>(outer_field_is_not_null, ((<cache>(<cache>(2)) = 2) or isnull(2)), true)) having (<if>(outer_field_is_not_null, <cache>(<is_not_null_test>(1)), true) and <if>(outer_field_is_not_null, <cache>(<is_not_null_test>(2)), true)))))) AS `(SELECT 1,2 FROM t2) NOT IN (SELECT 1,2 FROM t1)` from `test`.`t1`
 SELECT (SELECT 1,2 FROM t2) NOT IN (SELECT 1,2 FROM t1) FROM t1;
 (SELECT 1,2 FROM t2) NOT IN (SELECT 1,2 FROM t1)
 NULL
 DROP TABLE t1,t2;
+#
+# Bug#20729351 ASSERTION FAILED: ITEM_IN->LEFT_EXPR->ELEMENT_INDEX(0)->MAYBE_NULL
+#
+CREATE TABLE t1 (a LONGBLOB) ENGINE=INNODB;
+INSERT INTO t1 VALUES ('a'), ('a'), ('a');
+CREATE TABLE t2 (a INT) ENGINE=INNODB;
+INSERT INTO t2 VALUES(1), (1), (1), (1);
+ANALYZE TABLE t1, t2;
+Table	Op	Msg_type	Msg_text
+test.t1	analyze	status	OK
+test.t2	analyze	status	OK
+SELECT
+(SELECT NULL IN (NULL) FROM t1 WHERE a) =
+ANY(SELECT 1 FROM t2)
+FROM t1;
+(SELECT NULL IN (NULL) FROM t1 WHERE a) =
+ANY(SELECT 1 FROM t2)
+NULL
+NULL
+NULL
+DROP TABLE t1, t2;
 set @@optimizer_switch=@old_opt_switch;
 SET sql_mode = default;
 set global innodb_large_prefix=default;

mysql-test/r/subquery_mat_none.result

@@ -2051,11 +2051,32 @@ id	select_type	table	partitions	type	possible_keys	key	key_len	ref	rows	filtered
 3	DEPENDENT SUBQUERY	t1	NULL	ALL	NULL	NULL	NULL	NULL	1	100.00	NULL
 2	SUBQUERY	t2	NULL	ALL	NULL	NULL	NULL	NULL	1	100.00	NULL
 Warnings:
-Note	1003	/* select#1 */ select (not(<in_optimizer>((/* select#2 */ select 1,2 from `test`.`t2`),<exists>(/* select#3 */ select 1,1 from `test`.`t1` where 1 having 1)))) AS `(SELECT 1,2 FROM t2) NOT IN (SELECT 1,2 FROM t1)` from `test`.`t1`
+Note	1003	/* select#1 */ select (not(<in_optimizer>((/* select#2 */ select 1,2 from `test`.`t2`),<exists>(/* select#3 */ select 1,1 from `test`.`t1` where (<if>(outer_field_is_not_null, ((<cache>(<cache>(1)) = 1) or isnull(1)), true) and <if>(outer_field_is_not_null, ((<cache>(<cache>(2)) = 2) or isnull(2)), true)) having (<if>(outer_field_is_not_null, <cache>(<is_not_null_test>(1)), true) and <if>(outer_field_is_not_null, <cache>(<is_not_null_test>(2)), true)))))) AS `(SELECT 1,2 FROM t2) NOT IN (SELECT 1,2 FROM t1)` from `test`.`t1`
 SELECT (SELECT 1,2 FROM t2) NOT IN (SELECT 1,2 FROM t1) FROM t1;
 (SELECT 1,2 FROM t2) NOT IN (SELECT 1,2 FROM t1)
 NULL
 DROP TABLE t1,t2;
+#
+# Bug#20729351 ASSERTION FAILED: ITEM_IN->LEFT_EXPR->ELEMENT_INDEX(0)->MAYBE_NULL
+#
+CREATE TABLE t1 (a LONGBLOB) ENGINE=INNODB;
+INSERT INTO t1 VALUES ('a'), ('a'), ('a');
+CREATE TABLE t2 (a INT) ENGINE=INNODB;
+INSERT INTO t2 VALUES(1), (1), (1), (1);
+ANALYZE TABLE t1, t2;
+Table	Op	Msg_type	Msg_text
+test.t1	analyze	status	OK
+test.t2	analyze	status	OK
+SELECT
+(SELECT NULL IN (NULL) FROM t1 WHERE a) =
+ANY(SELECT 1 FROM t2)
+FROM t1;
+(SELECT NULL IN (NULL) FROM t1 WHERE a) =
+ANY(SELECT 1 FROM t2)
+NULL
+NULL
+NULL
+DROP TABLE t1, t2;
 set @@optimizer_switch=@old_opt_switch;
 SET sql_mode = default;
 set optimizer_switch=default;

sql/item.h

@@ -4884,15 +4884,15 @@ class Item_cache: public Item_basic_constant
     value_cached(0)
   {
     fixed= 1; 
-    null_value= 1;
+    maybe_null= null_value= 1;
   }
   Item_cache(enum_field_types field_type_arg):
     example(0), used_table_map(0), cached_field(0),
     cached_field_type(field_type_arg),
     value_cached(0)
   {
     fixed= 1;
-    null_value= 1;
+    maybe_null= null_value= 1;
   }
 
   void set_used_tables(table_map map) { used_table_map= map; }