Apply Jorgen Loland's fix: Bug#45221: Query "SELECT pk FROM C WHERE pk IN (SELECT int_key)" failing

XOR conditions are not optimized, and Item_cond_xor therefore
acts like type Func_item even though it inherits from Item_cond.
A subtle difference between Item_func and Item_cond is that
you can get the children Items from the former by calling
arguments(), and from the latter by calling argument_list().
However, since Item_cond_xor inherits from Item_cond,
arguments() did not return any Items.

The fact that Item_cond_xor::arguments() did not return it's
children items lead to a problem for make_cond_for_index();
the method accepted that XOR items on unindexed columns were
pushed using ICP. ICP evaluation of non-indexed columns
does not (and should not) work.

The fix for this bug is to make Item_cond_xor return it's
children items when the arguments() method is used. This makes
Item_cond_xor behave more like Item_func and in turn allows
make_cond_for_index() to discover any conflicting children
Items.

This is a temporary fix and should be removed when Item_cond_xor
 is optimized.

mysql-test/r/group_by.result

@@ -1542,8 +1542,8 @@ id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 EXPLAIN SELECT 1 FROM t1 WHERE a IN
 (SELECT a FROM t1 USE INDEX (i2) IGNORE INDEX (i2));
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
-1	PRIMARY	t1	index	NULL	PRIMARY	4	NULL	144	Using where; Using index
-2	DEPENDENT SUBQUERY	t1	ALL	NULL	NULL	NULL	NULL	144	Using where
+1	PRIMARY	t1	index	PRIMARY,i2	PRIMARY	4	NULL	144	Using index
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	144	Using where; FirstMatch(t1)
 CREATE TABLE t2 (a INT, b INT, KEY(a));
 INSERT INTO t2 VALUES (1, 1), (2, 2), (3,3), (4,4);
 EXPLAIN SELECT a, SUM(b) FROM t2 GROUP BY a LIMIT 2;
@@ -1555,8 +1555,8 @@ id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 EXPLAIN SELECT 1 FROM t2 WHERE a IN
 (SELECT a FROM t1 USE INDEX (i2) IGNORE INDEX (i2));
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
-1	PRIMARY	t2	index	NULL	a	5	NULL	4	Using where; Using index
-2	DEPENDENT SUBQUERY	t1	ALL	NULL	NULL	NULL	NULL	144	Using where
+1	PRIMARY	t2	index	a	a	5	NULL	4	Using index
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	144	Using where; FirstMatch(t2)
 SHOW VARIABLES LIKE 'old';
 Variable_name	Value
 old	OFF

sql/item_cmpfunc.h

@@ -1715,14 +1715,34 @@ inline bool is_cond_or(Item *item)
 class Item_cond_xor :public Item_cond
 {
 public:
-  Item_cond_xor() :Item_cond() {}
-  Item_cond_xor(Item *i1,Item *i2) :Item_cond(i1,i2) {}
+  Item_cond_xor(Item *i1,Item *i2) :Item_cond(i1,i2) 
+  {
+    /* 
+      Items must be stored in args[] as well because this Item_cond is
+      treated as a FUNC_ITEM (see type()). I.e., users of it will get
+      it's children by calling arguments(), not argument_list(). This
+      is a temporary solution until XOR is optimized and treated like
+      a full Item_cond citizen.
+     */
+    arg_count= 2;
+    args= tmp_arg;
+    args[0]= i1; 
+    args[1]= i2;
+  }
   enum Functype functype() const { return COND_XOR_FUNC; }
   /* TODO: remove the next line when implementing XOR optimization */
   enum Type type() const { return FUNC_ITEM; }
   longlong val_int();
   const char *func_name() const { return "xor"; }
   void top_level_item() {}
+  /* Since child Items are stored in args[], Items cannot be added.
+     However, since Item_cond_xor is treated as a FUNC_ITEM (see
+     type()), the methods below should never be called. 
+  */
+  bool add(Item *item) { DBUG_ASSERT(FALSE); return FALSE; }
+  bool add_at_head(Item *item) { DBUG_ASSERT(FALSE); return FALSE; }
+  bool add_at_head(List<Item> *nlist) { DBUG_ASSERT(FALSE); return FALSE; }
+  void copy_andor_arguments(THD *thd, Item_cond *item) { DBUG_ASSERT(FALSE); }
 };