BUG#18492: mysqld reports ER_ILLEGAL_REFERENCE in --ps-protocol

In the code that converts IN predicates to EXISTS predicates it is changing
the select list elements to constant 1. Example :
SELECT ... FROM ...  WHERE a IN (SELECT c FROM ...)
is transformed to :
SELECT ... FROM ... WHERE EXISTS (SELECT 1 FROM ...  HAVING a = c)
However there can be no FROM clause in the IN subquery and it may not be
a simple select : SELECT ... FROM ... WHERE a IN (SELECT f(..) AS
c UNION SELECT ...) This query is transformed to : SELECT ... FROM ...
WHERE EXISTS (SELECT 1 FROM (SELECT f(..) AS c UNION SELECT ...)
x HAVING a = c) In the above query c in the HAVING clause is made to be
an Item_null_helper (a subclass of Item_ref) pointing to the real
Item_field (which is not referenced anywhere else in the query anymore).
This is done because Item_ref_null_helper collects information whether
there are NULL values in the result.  This is OK for directly executed
statements, because the Item_field pointed by the Item_null_helper is
already fixed when the transformation is done.  But when executed as
a prepared statement all the Item instances are "un-fixed" before the
recompilation of the prepared statement. So when the Item_null_helper
gets fixed it discovers that the Item_field it points to is not fixed
and issues an error.  The remedy is to keep the original select list
references when there are no tables in the FROM clause. So the above
becomes : SELECT ... FROM ...  WHERE EXISTS (SELECT c FROM (SELECT f(..)
AS c UNION SELECT ...) x HAVING a = c) In this way c is referenced
directly in the select list as well as by reference in the HAVING
clause. So it gets correctly fixed even with prepared statements.  And
since the Item_null_helper subclass of Item_ref_null_helper is not used
anywhere else it's taken out.

mysql-test/r/ps_11bugs.result

@@ -116,3 +116,17 @@ execute st_1676 using @arg0, @arg1, @arg2;
 cola	colb	cold
 aaaa	yyyy	R
 drop table t1, t2;
+create table t1 (a int primary key);
+insert into t1 values (1);
+explain select * from t1 where 3 in (select (1+1) union select 1);
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Impossible WHERE noticed after reading const tables
+2	DEPENDENT SUBQUERY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	No tables used
+3	DEPENDENT UNION	NULL	NULL	NULL	NULL	NULL	NULL	NULL	No tables used
+NULL	UNION RESULT	<union2,3>	ALL	NULL	NULL	NULL	NULL	NULL	
+select * from t1 where 3 in (select (1+1) union select 1);
+a
+prepare st_18492 from 'select * from t1 where 3 in (select (1+1) union select 1)';
+execute st_18492;
+a
+drop table t1;

mysql-test/r/subselect.result

@@ -734,7 +734,7 @@ id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 3	DEPENDENT UNION	NULL	NULL	NULL	NULL	NULL	NULL	NULL	No tables used
 NULL	UNION RESULT	<union2,3>	ALL	NULL	NULL	NULL	NULL	NULL	
 Warnings:
-Note	1003	select test.t2.id AS `id` from test.t2 where <in_optimizer>(test.t2.id,<exists>(select 1 AS `Not_used` having (<cache>(test.t2.id) = <null_helper>(1)) union select 1 AS `Not_used` having (<cache>(test.t2.id) = <null_helper>(3))))
+Note	1003	select test.t2.id AS `id` from test.t2 where <in_optimizer>(test.t2.id,<exists>(select 1 AS `1` having (<cache>(test.t2.id) = <ref_null_helper>(1)) union select 3 AS `3` having (<cache>(test.t2.id) = <ref_null_helper>(3))))
 SELECT * FROM t2 WHERE id IN (SELECT 5 UNION SELECT 3);
 id
 SELECT * FROM t2 WHERE id IN (SELECT 5 UNION SELECT 2);

mysql-test/t/ps_11bugs.test

@@ -130,3 +130,17 @@ drop table t1, t2;
 # end of bug#1676
 
 # End of 4.1 tests
+
+# bug#18492: mysqld reports ER_ILLEGAL_REFERENCE in --ps-protocol
+
+create table t1 (a int primary key);
+insert into t1 values (1);
+
+explain select * from t1 where 3 in (select (1+1) union select 1);
+
+select * from t1 where 3 in (select (1+1) union select 1);
+
+prepare st_18492 from 'select * from t1 where 3 in (select (1+1) union select 1)';
+execute st_18492;
+
+drop table t1;

sql/item.cc

@@ -2716,14 +2716,6 @@ void Item_ref_null_helper::print(String *str)
 }
 
 
-void Item_null_helper::print(String *str)
-{
-  str->append("<null_helper>(", 14);
-  store->print(str);
-  str->append(')');
-}
-
-
 bool Item_default_value::eq(const Item *item, bool binary_cmp) const
 {
   return item->type() == DEFAULT_VALUE_ITEM && 

sql/item.h

@@ -1045,19 +1045,6 @@ public:
   }
 };
 
-class Item_null_helper :public Item_ref_null_helper
-{
-  Item *store;
-public:
-  Item_null_helper(Item_in_subselect* master, Item *item,
-		   const char *table_name_par, const char *field_name_par)
-    :Item_ref_null_helper(master, &item, table_name_par, field_name_par),
-     store(item)
-    { ref= &store; }
-  void print(String *str);
-};
-
-
 /*
   The following class is used to optimize comparing of date and bigint columns
   We need to save the original item ('ref') to be able to call

sql/item_subselect.cc

@@ -822,13 +822,13 @@ Item_in_subselect::single_value_transformer(JOIN *join,
   }
   else
   {
-    select_lex->item_list.empty();
-    select_lex->item_list.push_back(new Item_int("Not_used",
-						 (longlong) 1, 21));
-    select_lex->ref_pointer_array[0]= select_lex->item_list.head();
     if (select_lex->table_list.elements)
     {
       Item *having= item, *orig_item= item;
+      select_lex->item_list.empty();
+      select_lex->item_list.push_back(new Item_int("Not_used",
+                                                   (longlong) 1, 21));
+      select_lex->ref_pointer_array[0]= select_lex->item_list.head();
       item= func->create(expr, item);
       if (!abort_on_null && orig_item->maybe_null)
       {
@@ -875,9 +875,11 @@ Item_in_subselect::single_value_transformer(JOIN *join,
 	select_lex->having=
 	  join->having=
 	  func->create(expr,
-		       new Item_null_helper(this, item,
-					    (char *)"<no matter>",
-					    (char *)"<result>"));
+                       new Item_ref_null_helper(this,
+                                            select_lex->ref_pointer_array,
+                                            (char *)"<no matter>",
+                                            (char *)"<result>"));
+
 	select_lex->having_fix_field= 1;
 	if (join->having->fix_fields(thd, join->tables_list,
 				     0))