MWL#89: Cost-based choice between Materialization and IN->EXISTS transformation

- Corrected a wrong result that was recorded by the MySQL fix for BUG#39069.

- Removed Item_func_isnull::cached_value and all the logic around this custom-made
  caching of the NULL result because MWL#89 optimizes subqueries before the outer
  query is being executed, and this cache cannot be made easily to work for all
  kinds of Items (specifically Item_sum_sum, but others too).

1 files changed, 0 insertions, 11 deletions

diff --git a/sql/item_cmpfunc.h b/sql/item_cmpfunc.h
index e161c1baa84..33407a161b8 100644
--- a/sql/item_cmpfunc.h
+++ b/sql/item_cmpfunc.h
@@ -1304,8 +1304,6 @@ public:
 
 class Item_func_isnull :public Item_bool_func
 {
-protected:
-  longlong cached_value;
 public:
   Item_func_isnull(Item *a) :Item_bool_func(a) {}
   longlong val_int();
@@ -1323,18 +1321,9 @@ public:
     {
       used_tables_cache= 0;			/* is always false */
       const_item_cache= 1;
-      cached_value= (longlong) 0;
     }
     else
-    {
       args[0]->update_used_tables();
-      if ((const_item_cache= !(used_tables_cache= args[0]->used_tables())) &&
-          !with_subselect)
-      {
-	/* Remember if the value is always NULL or never NULL */
-	cached_value= (longlong) args[0]->is_null();
-      }
-    }
   }
   table_map not_null_tables() const { return 0; }
   optimize_type select_optimize() const { return OPTIMIZE_NULL; }