new optimisation for ref_null (SCRUM) (WL#818)

mysql-test/r/subselect.result:
  results of new optimisation
mysql-test/t/subselect.test:
  results of new optimisation
sql/item_cmpfunc.h:
  function type
sql/item_func.h:
  function type
sql/item_subselect.cc:
  new optimisation for ref_or_null
sql/item_subselect.h:
  new optimisation for ref_or_null
sql/sql_select.cc:
  new optimisation for ref_or_null
sql/sql_select.h:
  item_subselect.cc need safe_index_read

1 files changed, 6 insertions, 2 deletions

diff --git a/sql/item_subselect.h b/sql/item_subselect.h
index 5749220629f..e2738102ebd 100644
--- a/sql/item_subselect.h
+++ b/sql/item_subselect.h
@@ -228,6 +228,7 @@ public:
   friend class Item_asterisk_remover;
   friend class Item_ref_null_helper;
   friend class Item_is_not_null_test;
+  friend class subselect_indexin_engine;
 };
 
 /* ALL/ANY/SOME subselect */
@@ -337,10 +338,13 @@ public:
 
 class subselect_indexin_engine: public subselect_simplein_engine
 {
+  bool check_null;
 public:
   subselect_indexin_engine(THD *thd, st_join_table *tab_arg,
-			    Item_subselect *subs, Item *where)
-    :subselect_simplein_engine(thd, tab_arg, subs, where)
+			    Item_subselect *subs, Item *where,
+			   bool chk_null)
+    :subselect_simplein_engine(thd, tab_arg, subs, where),
+     check_null(chk_null)
   {}
   int exec();
 };