Fix bug #14816 test_if_order_by_key() expected only Item_fields.

test_if_order_by_key() expected only Item_fields to be in order->item, thus
failing to find available index on view's field, which results in reported
error.

Now test_if_order_by_key() calls order->item->real_item() to get field for
choosing index.

mysql-test/r/view.result

@@ -2385,3 +2385,11 @@ show create view v1;
 View	Create View
 v1	CREATE ALGORITHM=UNDEFINED DEFINER=`root`@`localhost` SQL SECURITY INVOKER VIEW `v1` AS select 1 AS `1`
 drop view v1;
+create table t1 (id INT, primary key(id));
+insert into t1 values (1),(2);
+create view v1 as select * from t1;
+explain select id from v1 order by id;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	index	NULL	PRIMARY	4	NULL	2	Using index
+drop view v1;
+drop table t1;

mysql-test/t/view.test

@@ -2253,3 +2253,13 @@ drop view v1;
 create definer = current_user sql security invoker view v1 as select 1;
 show create view v1;
 drop view v1;
+
+#
+# Bug #14816 test_if_order_by_key() expected only Item_fields.
+#
+create table t1 (id INT, primary key(id));
+insert into t1 values (1),(2);
+create view v1 as select * from t1;
+explain select id from v1 order by id;
+drop view v1;
+drop table t1;

sql/sql_select.cc

@@ -10988,7 +10988,7 @@ static int test_if_order_by_key(ORDER *order, TABLE *table, uint idx,
 
   for (; order ; order=order->next, const_key_parts>>=1)
   {
-    Field *field=((Item_field*) (*order->item))->field;
+    Field *field=((Item_field*) (*order->item)->real_item())->field;
     int flag;
 
     /*