Bug#37560280 Incorrect behavior with EXPLAIN and subqueries

EXPLAIN could execute a stored function in a subquery when the subquery created a derived table, e.g.: EXPLAIN SELECT * FROM (SELECT f()) AS a; This issue was caused by Table_ref::materializable_is_const(), which incorrectly treated a function call as a constant expression. Now, we ensure that a derived table subquery containing a stored function call is not considered constant. Change-Id: Id73d567b3617da1523996e8ee0ed73b4879451ad (cherry picked from commit 2830b52f5515af4f7e9330492593446b215b004a)

Author: Volodymyr Verovkin

mysql-test/r/partition_locking.result

@@ -5030,9 +5030,9 @@ Handler_read_next	12
 UNLOCK TABLES;
 EXPLAIN SELECT * FROM t2 WHERE a = sf_a_from_t1b_d('1');
 id	select_type	table	partitions	type	possible_keys	key	key_len	ref	rows	filtered	Extra
-1	SIMPLE	t2p1	constPRIMARY	PRIMARY	4	const	#	100.00NULL
+1	SIMPLE	t2p0,p1,p2	eq_refPRIMARY	PRIMARY	4	const	#	100.00Using where
 Warnings:
-Note	1003	/* select#1 */ select '1' AS `a`,'1' AS `b` from `test`.`t2` where true
+Note	1003	/* select#1 */ select `test`.`t2`.`a` AS `a`,`test`.`t2`.`b` AS `b` from `test`.`t2` where (`test`.`t2`.`a` = <cache>(`sf_a_from_t1b_d`('1')))
 FLUSH STATUS;
 START TRANSACTION;
 SELECT * FROM t2 WHERE a = sf_a_from_t1b_d('1');
@@ -5086,9 +5086,9 @@ Handler_read_next	12
 UNLOCK TABLES;
 EXPLAIN SELECT * FROM t2 WHERE a = 7 + sf_a_from_t1b_d('1');
 id	select_type	table	partitions	type	possible_keys	key	key_len	ref	rows	filtered	Extra
-1	SIMPLE	t2	p2constPRIMARY	PRIMARY	4	const	#	100.00NULL
+1	SIMPLE	t2p0,p1,p2eq_refPRIMARY	PRIMARY	4	const	#	100.00Using where
 Warnings:
-Note	1003	/* select#1 */ select '8' AS `a`,'8' AS `b` from `test`.`t2` where true
+Note	1003	/* select#1 */ select `test`.`t2`.`a` AS `a`,`test`.`t2`.`b` AS `b` from `test`.`t2` where (`test`.`t2`.`a` = <cache>((7 + `sf_a_from_t1b_d`('1'))))
 FLUSH STATUS;
 START TRANSACTION;
 SELECT * FROM t2 WHERE a = 7 + sf_a_from_t1b_d('1');
@@ -5138,9 +5138,9 @@ Handler_read_next	7
 UNLOCK TABLES;
 EXPLAIN SELECT * FROM t2 WHERE a = sf_a_from_t1b_d('1') AND a = 2;
 id	select_type	table	partitions	type	possible_keys	key	key_len	ref	rows	filtered	Extra
-1	SIMPLENULL	NULL	NULL	NULL	NULL	NULL	NULL#NULL	Impossible WHERE
+1	SIMPLEt2	p2	const	PRIMARY	PRIMARY	4	const#100.00	NULL
 Warnings:
-Note	1003	/* select#1 */ select `test`.`t2`.`a` AS `a`,`test`.`t2`.`b` AS `b` from `test`.`t2` where false
+Note	1003	/* select#1 */ select '2' AS `a`,'2' AS `b` from `test`.`t2` where ((2 = `sf_a_from_t1b_d`('1')))
 FLUSH STATUS;
 START TRANSACTION;
 SELECT * FROM t2 WHERE a = sf_a_from_t1b_d('1') AND a = 2;
@@ -5322,9 +5322,9 @@ Handler_read_next	12
 UNLOCK TABLES;
 EXPLAIN SELECT sf_add_1(a) - 1, sf_add_hello(b) FROM t2 WHERE a = sf_a_from_t1b_d('1');
 id	select_type	table	partitions	type	possible_keys	key	key_len	ref	rows	filtered	Extra
-1	SIMPLE	t2p1	constPRIMARY	PRIMARY	4	const	#	100.00NULL
+1	SIMPLE	t2p0,p1,p2	eq_refPRIMARY	PRIMARY	4	const	#	100.00Using where
 Warnings:
-Note	1003	/* select#1 */ select (`sf_add_1`('1') - 1) AS `sf_add_1(a) - 1`,`sf_add_hello`('1') AS `sf_add_hello(b)` from `test`.`t2` where true
+Note	1003	/* select#1 */ select (`sf_add_1`(`test`.`t2`.`a`) - 1) AS `sf_add_1(a) - 1`,`sf_add_hello`(`test`.`t2`.`b`) AS `sf_add_hello(b)` from `test`.`t2` where (`test`.`t2`.`a` = <cache>(`sf_a_from_t1b_d`('1')))
 FLUSH STATUS;
 START TRANSACTION;
 SELECT sf_add_1(a) - 1, sf_add_hello(b) FROM t2 WHERE a = sf_a_from_t1b_d('1');
@@ -5378,9 +5378,9 @@ Handler_read_next	12
 UNLOCK TABLES;
 EXPLAIN SELECT sf_add_1(a) - 1, sf_add_hello(b) FROM t2 WHERE a = 7 + sf_a_from_t1b_d('1');
 id	select_type	table	partitions	type	possible_keys	key	key_len	ref	rows	filtered	Extra
-1	SIMPLE	t2	p2constPRIMARY	PRIMARY	4	const	#	100.00NULL
+1	SIMPLE	t2p0,p1,p2eq_refPRIMARY	PRIMARY	4	const	#	100.00Using where
 Warnings:
-Note	1003	/* select#1 */ select (`sf_add_1`('8') - 1) AS `sf_add_1(a) - 1`,`sf_add_hello`('8') AS `sf_add_hello(b)` from `test`.`t2` where true
+Note	1003	/* select#1 */ select (`sf_add_1`(`test`.`t2`.`a`) - 1) AS `sf_add_1(a) - 1`,`sf_add_hello`(`test`.`t2`.`b`) AS `sf_add_hello(b)` from `test`.`t2` where (`test`.`t2`.`a` = <cache>((7 + `sf_a_from_t1b_d`('1'))))
 FLUSH STATUS;
 START TRANSACTION;
 SELECT sf_add_1(a) - 1, sf_add_hello(b) FROM t2 WHERE a = 7 + sf_a_from_t1b_d('1');
@@ -5430,9 +5430,9 @@ Handler_read_next	7
 UNLOCK TABLES;
 EXPLAIN SELECT sf_add_1(a) - 1, sf_add_hello(b) FROM t2 WHERE a = sf_a_from_t1b_d('1') AND a = 2;
 id	select_type	table	partitions	type	possible_keys	key	key_len	ref	rows	filtered	Extra
-1	SIMPLENULL	NULL	NULL	NULL	NULL	NULL	NULL#NULL	Impossible WHERE
+1	SIMPLEt2	p2	const	PRIMARY	PRIMARY	4	const#100.00	NULL
 Warnings:
-Note	1003	/* select#1 */ select (`sf_add_1`(`test`.`t2`.`a`) - 1) AS `sf_add_1(a) - 1`,`sf_add_hello`(`test`.`t2`.`b`) AS `sf_add_hello(b)` from `test`.`t2` where false
+Note	1003	/* select#1 */ select (`sf_add_1`('2') - 1) AS `sf_add_1(a) - 1`,`sf_add_hello`('2') AS `sf_add_hello(b)` from `test`.`t2` where ((2 = `sf_a_from_t1b_d`('1')))
 FLUSH STATUS;
 START TRANSACTION;
 SELECT sf_add_1(a) - 1, sf_add_hello(b) FROM t2 WHERE a = sf_a_from_t1b_d('1') AND a = 2;
@@ -5652,7 +5652,7 @@ ROLLBACK;
 UNLOCK TABLES;
 EXPLAIN UPDATE t2 SET b = CONCAT('+', b) WHERE a = sf_a_from_t1b_d('1');
 id	select_type	table	partitions	type	possible_keys	key	key_len	ref	rows	filtered	Extra
-1	UPDATE	t2p1	range	PRIMARYPRIMARY	4const#	100.00	Using where
+1	UPDATE	t2p0,p1,p2	index	NULLPRIMARY	4NULL#	100.00	Using where
 Warnings:
 Note	1003	update `test`.`t2` set `test`.`t2`.`b` = concat('+',`test`.`t2`.`b`) where (`test`.`t2`.`a` = `sf_a_from_t1b_d`('1'))
 FLUSH STATUS;
@@ -5734,7 +5734,7 @@ ROLLBACK;
 UNLOCK TABLES;
 EXPLAIN UPDATE t2 SET b = CONCAT('+', b) WHERE a = 7 + sf_a_from_t1b_d('1');
 id	select_type	table	partitions	type	possible_keys	key	key_len	ref	rows	filtered	Extra
-1	UPDATE	t2	p2range	PRIMARYPRIMARY	4const#	100.00	Using where
+1	UPDATE	t2p0,p1,p2index	NULLPRIMARY	4NULL#	100.00	Using where
 Warnings:
 Note	1003	update `test`.`t2` set `test`.`t2`.`b` = concat('+',`test`.`t2`.`b`) where (`test`.`t2`.`a` = (7 + `sf_a_from_t1b_d`('1')))
 FLUSH STATUS;
@@ -5808,9 +5808,9 @@ ROLLBACK;
 UNLOCK TABLES;
 EXPLAIN UPDATE t2 SET b = CONCAT('+', b) WHERE a = sf_a_from_t1b_d('1') AND a = 2;
 id	select_type	table	partitions	type	possible_keys	key	key_len	ref	rows	filtered	Extra
-1	UPDATENULL	NULL	NULL	NULL	NULL	NULL	NULL#NULL	Impossible WHERE
+1	UPDATEt2	p2	range	PRIMARY	PRIMARY	4	const#100.00	Using where
 Warnings:
-Note	1003	update `test`.`t2` set `test`.`t2`.`b` = concat('+',`test`.`t2`.`b`) where ()
+Note	1003	update `test`.`t2` set `test`.`t2`.`b` = concat('+',`test`.`t2`.`b`) where ((`test`.`t2`.`a` = 2) and (2 = `sf_a_from_t1b_d`('1')))
 FLUSH STATUS;
 START TRANSACTION;
 UPDATE t2 SET b = CONCAT('+', b) WHERE a = sf_a_from_t1b_d('1') AND a = 2;
@@ -6064,7 +6064,7 @@ ROLLBACK;
 UNLOCK TABLES;
 EXPLAIN UPDATE t2 SET b = sf_add_hello(b) WHERE a = sf_a_from_t1b_d('1');
 id	select_type	table	partitions	type	possible_keys	key	key_len	ref	rows	filtered	Extra
-1	UPDATE	t2p1	range	PRIMARYPRIMARY	4const#	100.00	Using where
+1	UPDATE	t2p0,p1,p2	index	NULLPRIMARY	4NULL#	100.00	Using where
 Warnings:
 Note	1003	update `test`.`t2` set `test`.`t2`.`b` = `sf_add_hello`(`test`.`t2`.`b`) where (`test`.`t2`.`a` = `sf_a_from_t1b_d`('1'))
 FLUSH STATUS;
@@ -6146,7 +6146,7 @@ ROLLBACK;
 UNLOCK TABLES;
 EXPLAIN UPDATE t2 SET b = sf_add_hello(b) WHERE a = 7 + sf_a_from_t1b_d('1');
 id	select_type	table	partitions	type	possible_keys	key	key_len	ref	rows	filtered	Extra
-1	UPDATE	t2	p2range	PRIMARYPRIMARY	4const#	100.00	Using where
+1	UPDATE	t2p0,p1,p2index	NULLPRIMARY	4NULL#	100.00	Using where
 Warnings:
 Note	1003	update `test`.`t2` set `test`.`t2`.`b` = `sf_add_hello`(`test`.`t2`.`b`) where (`test`.`t2`.`a` = (7 + `sf_a_from_t1b_d`('1')))
 FLUSH STATUS;
@@ -6220,9 +6220,9 @@ ROLLBACK;
 UNLOCK TABLES;
 EXPLAIN UPDATE t2 SET b = sf_add_hello(b) WHERE a = sf_a_from_t1b_d('1') AND a = 2;
 id	select_type	table	partitions	type	possible_keys	key	key_len	ref	rows	filtered	Extra
-1	UPDATENULL	NULL	NULL	NULL	NULL	NULL	NULL#NULL	Impossible WHERE
+1	UPDATEt2	p2	range	PRIMARY	PRIMARY	4	const#100.00	Using where
 Warnings:
-Note	1003	update `test`.`t2` set `test`.`t2`.`b` = `sf_add_hello`(`test`.`t2`.`b`) where ()
+Note	1003	update `test`.`t2` set `test`.`t2`.`b` = `sf_add_hello`(`test`.`t2`.`b`) where ((`test`.`t2`.`a` = 2) and (2 = `sf_a_from_t1b_d`('1')))
 FLUSH STATUS;
 START TRANSACTION;
 UPDATE t2 SET b = sf_add_hello(b) WHERE a = sf_a_from_t1b_d('1') AND a = 2;
@@ -6482,7 +6482,7 @@ ROLLBACK;
 UNLOCK TABLES;
 EXPLAIN UPDATE t2 SET a = sf_add_1(a) + 4 WHERE a = sf_a_from_t1b_d('1');
 id	select_type	table	partitions	type	possible_keys	key	key_len	ref	rows	filtered	Extra
-1	UPDATE	t2p1	range	PRIMARYPRIMARY	4const#	100.00	Using where
+1	UPDATE	t2p0,p1,p2	index	NULLPRIMARY	4NULL#	100.00	Using where; Using temporary
 Warnings:
 Note	1003	update `test`.`t2` set `test`.`t2`.`a` = (`sf_add_1`(`test`.`t2`.`a`) + 4) where (`test`.`t2`.`a` = `sf_a_from_t1b_d`('1'))
 FLUSH STATUS;
@@ -6568,7 +6568,7 @@ ROLLBACK;
 UNLOCK TABLES;
 EXPLAIN UPDATE t2 SET a = sf_add_1(a) + 4 WHERE a = 7 + sf_a_from_t1b_d('1');
 id	select_type	table	partitions	type	possible_keys	key	key_len	ref	rows	filtered	Extra
-1	UPDATE	t2	p2range	PRIMARYPRIMARY	4const#	100.00	Using where
+1	UPDATE	t2p0,p1,p2index	NULLPRIMARY	4NULL#	100.00	Using where; Using temporary
 Warnings:
 Note	1003	update `test`.`t2` set `test`.`t2`.`a` = (`sf_add_1`(`test`.`t2`.`a`) + 4) where (`test`.`t2`.`a` = (7 + `sf_a_from_t1b_d`('1')))
 FLUSH STATUS;
@@ -6644,9 +6644,9 @@ ROLLBACK;
 UNLOCK TABLES;
 EXPLAIN UPDATE t2 SET a = sf_add_1(a) + 4 WHERE a = sf_a_from_t1b_d('1') AND a = 2;
 id	select_type	table	partitions	type	possible_keys	key	key_len	ref	rows	filtered	Extra
-1	UPDATENULL	NULL	NULL	NULL	NULL	NULL	NULL#NULL	Impossible WHERE
+1	UPDATEt2	p2	range	PRIMARY	PRIMARY	4	const#100.00	Using where
 Warnings:
-Note	1003	update `test`.`t2` set `test`.`t2`.`a` = (`sf_add_1`(`test`.`t2`.`a`) + 4) where ()
+Note	1003	update `test`.`t2` set `test`.`t2`.`a` = (`sf_add_1`(`test`.`t2`.`a`) + 4) where ((`test`.`t2`.`a` = 2) and (2 = `sf_a_from_t1b_d`('1')))
 FLUSH STATUS;
 START TRANSACTION;
 UPDATE t2 SET a = sf_add_1(a) + 4 WHERE a = sf_a_from_t1b_d('1') AND a = 2;
@@ -6899,7 +6899,7 @@ ROLLBACK;
 UNLOCK TABLES;
 EXPLAIN DELETE FROM t2 WHERE a = sf_a_from_t1b_d('1');
 id	select_type	table	partitions	type	possible_keys	key	key_len	ref	rows	filtered	Extra
-1	DELETE	t2p1	range	PRIMARY	PRIMARY	4	const#	100.00	Using where
+1	DELETE	t2p0,p1,p2	ALL	NULL	NULL	NULL	NULL#	100.00	Using where
 Warnings:
 Note	1003	delete from `test`.`t2` where (`test`.`t2`.`a` = `sf_a_from_t1b_d`('1'))
 FLUSH STATUS;
@@ -6977,7 +6977,7 @@ ROLLBACK;
 UNLOCK TABLES;
 EXPLAIN DELETE FROM t2 WHERE a = 7 + sf_a_from_t1b_d('1');
 id	select_type	table	partitions	type	possible_keys	key	key_len	ref	rows	filtered	Extra
-1	DELETE	t2	p2range	PRIMARY	PRIMARY	4	const#	100.00	Using where
+1	DELETE	t2p0,p1,p2ALL	NULL	NULL	NULL	NULL#	100.00	Using where
 Warnings:
 Note	1003	delete from `test`.`t2` where (`test`.`t2`.`a` = (7 + `sf_a_from_t1b_d`('1')))
 FLUSH STATUS;
@@ -7049,9 +7049,9 @@ ROLLBACK;
 UNLOCK TABLES;
 EXPLAIN DELETE FROM t2 WHERE a = sf_a_from_t1b_d('1') AND a = 2;
 id	select_type	table	partitions	type	possible_keys	key	key_len	ref	rows	filtered	Extra
-1	DELETENULL	NULL	NULL	NULL	NULL	NULL	NULL#NULL	Impossible WHERE
+1	DELETEt2	p2	range	PRIMARY	PRIMARY	4	const#100.00	Using where
 Warnings:
-Note	1003	delete from `test`.`t2` where ()
+Note	1003	delete from `test`.`t2` where ((`test`.`t2`.`a` = 2) and (2 = `sf_a_from_t1b_d`('1')))
 FLUSH STATUS;
 START TRANSACTION;
 DELETE FROM t2 WHERE a = sf_a_from_t1b_d('1') AND a = 2;

mysql-test/r/sp.result

@@ -6377,24 +6377,24 @@ Warnings:
 Note	1003	/* select#1 */ select `test`.`t1`.`c1` AS `c1` from `test`.`t1` where (`test`.`t1`.`c1` = 1)
 EXPLAIN SELECT * FROM t1 WHERE c1=f1();
 id	select_type	table	partitions	type	possible_keys	key	key_len	ref	rows	filtered	Extra
-1	SIMPLE	t1	NULL	ref	c1	c1	5	const	1	100.00	Using index
+1	SIMPLE	t1	NULL	ref	c1	c1	5	const	1	100.00	Using where; Using index
 Warnings:
-Note	1003	/* select#1 */ select `test`.`t1`.`c1` AS `c1` from `test`.`t1` where (`test`.`t1`.`c1` = `f1`())
+Note	1003	/* select#1 */ select `test`.`t1`.`c1` AS `c1` from `test`.`t1` where (`test`.`t1`.`c1` = <cache>(`f1`()))
 EXPLAIN SELECT * FROM v1 WHERE c1=1;
 id	select_type	table	partitions	type	possible_keys	key	key_len	ref	rows	filtered	Extra
 1	SIMPLE	t1	NULL	ref	c1	c1	5	const	1	100.00	Using index
 Warnings:
 Note	1003	/* select#1 */ select `test`.`t1`.`c1` AS `c1` from `test`.`t1` where (`test`.`t1`.`c1` = 1)
 EXPLAIN SELECT * FROM v1 WHERE c1=f1();
 id	select_type	table	partitions	type	possible_keys	key	key_len	ref	rows	filtered	Extra
-1	SIMPLE	t1	NULL	ref	c1	c1	5	const	1	100.00	Using index
+1	SIMPLE	t1	NULL	ref	c1	c1	5	const	1	100.00	Using where; Using index
 Warnings:
-Note	1003	/* select#1 */ select `test`.`t1`.`c1` AS `c1` from `test`.`t1` where (`test`.`t1`.`c1` = `f1`())
+Note	1003	/* select#1 */ select `test`.`t1`.`c1` AS `c1` from `test`.`t1` where (`test`.`t1`.`c1` = <cache>(`f1`()))
 EXPLAIN SELECT * FROM t1 WHERE c1=f2(10);
 id	select_type	table	partitions	type	possible_keys	key	key_len	ref	rows	filtered	Extra
-1	SIMPLE	t1	NULL	ref	c1	c1	5	const	1	100.00	Using index
+1	SIMPLE	t1	NULL	ref	c1	c1	5	const	1	100.00	Using where; Using index
 Warnings:
-Note	1003	/* select#1 */ select `test`.`t1`.`c1` AS `c1` from `test`.`t1` where (`test`.`t1`.`c1` = `f2`(10))
+Note	1003	/* select#1 */ select `test`.`t1`.`c1` AS `c1` from `test`.`t1` where (`test`.`t1`.`c1` = <cache>(`f2`(10)))
 EXPLAIN SELECT * FROM t1 WHERE c1=f2(c1);
 id	select_type	table	partitions	type	possible_keys	key	key_len	ref	rows	filtered	Extra
 1	SIMPLE	t1	NULL	index	NULL	c1	5	NULL	5	20.00	Using where; Using index

mysql-test/t/partition_locking.test

@@ -2938,6 +2938,11 @@ DROP TABLE t1, t2;
 --echo #
 --echo # Test subqueries/stored functions with UPDATE/DELETE/SELECT
 --echo #
+# Bug#37560280:
+# The EXPLAIN plan for queries with the sf_a_from_t1b_d() function call
+# differs from the actual execution plan because constant folding
+# is performed in the actual plan but not in EXPLAIN.
+
 CREATE TABLE tq (id int PRIMARY KEY auto_increment, query varchar(255), not_select tinyint);
 CREATE TABLE tsq (id int PRIMARY KEY auto_increment, subquery varchar(255), can_be_locked tinyint);
 CREATE TABLE t1 (a int, b varchar(255), PRIMARY KEY (a), KEY (b))

sql/item.h

@@ -3594,6 +3594,15 @@ inline bool WalkItem(Item *item, enum_walk walk, T &&functor) {
  reinterpret_cast<uchar *>(&functor));
 }
 
+/**
+ Overload for const 'item' and functor taking 'const Item*' argument.
+*/
+template <class T>
+inline bool WalkItem(const Item *item, enum_walk walk, T &&functor) {
+ auto to_const = [&](const Item *descendant) { return functor(descendant); };
+ return WalkItem(const_cast<Item *>(item), walk, to_const);
+}
+
 /**
  Same as WalkItem, but for Item::compile(). Use as e.g.:
 

sql/item_func.cc

@@ -8192,6 +8192,8 @@ bool Item_func_sp::val_json(Json_wrapper *result) {
 bool Item_func_sp::execute() {
  THD *thd = current_thd;
 
+ assert(!thd->lex->is_explain() || thd->lex->is_explain_analyze);
+
  Internal_error_handler_holder<View_error_handler, Table_ref> view_handler(
  thd, context->view_error_handler, context->view_error_handler_arg);
 

sql/sql_derived.cc

@@ -1623,7 +1623,7 @@ bool Table_ref::optimize_derived(THD *thd) {
  // at execution time (in fact, it will get confused and crash if it has
  // already been materialized).
  if (!thd->lex->using_hypergraph_optimizer()) {
- if (materializable_is_const() &&
+ if (materializable_is_const(thd) &&
  (create_materialized_table(thd) || materialize_derived(thd)))
  return true;
  }

sql/sql_lex.h

@@ -726,6 +726,8 @@ class Query_expression {
  bool prepared; ///< All query blocks in query expression are prepared
  bool optimized; ///< All query blocks in query expression are optimized
  bool executed; ///< Query expression has been executed
+ ///< Explain mode: query expression refers stored function
+ bool m_has_stored_program{false};
 
  /// Object to which the result for this query expression is sent.
  /// Not used if we materialize directly into a parent query expression's
@@ -770,6 +772,8 @@ class Query_expression {
  /// multi-level ORDER, i.e. we have a "simple table".
  bool is_simple() const { return m_query_term->term_type() == QT_QUERY_BLOCK; }
 
+ bool has_stored_program() const { return m_has_stored_program; }
+
  /// Values for Query_expression::cleaned
  enum enum_clean_state {
  UC_DIRTY, ///< Unit isn't cleaned
@@ -4825,4 +4829,12 @@ bool accept_for_join(mem_root_deque<Table_ref *> *tables,
 Table_ref *nest_join(THD *thd, Query_block *select, Table_ref *embedding,
  mem_root_deque<Table_ref *> *jlist, size_t table_cnt,
  const char *legend);
+
+template <typename T>
+inline bool WalkQueryExpression(Query_expression *query_expr, enum_walk walk,
+ T &&functor) {
+ return query_expr->walk(&Item::walk_helper_thunk<T>, walk,
+ reinterpret_cast<uchar *>(&functor));
+}
+
 #endif /* SQL_LEX_INCLUDED */