Fix bug lp:1002079

  
  Analysis:
  The optimizer detects an empty result through constant table optimization.
  Then it calls return_zero_rows(), which in turns calls inderctly
  Item_maxmin_subselect::no_rows_in_result(). The latter method set "value=0",
  however "value" is pointer to Item_cache, and not just an integer value.
  
  All of the Item_[maxmin | singlerow]_subselect::val_XXX methods does:
    if (forced_const)
      return value->val_real();
  which of course crashes when value is a NULL pointer.
  
  Solution:
  When the optimizer discovers an empty result set, set
  Item_singlerow_subselect::value to a FALSE constant Item instead of NULL.

1 files changed, 1 insertions, 1 deletions

diff --git a/sql/item_subselect.h b/sql/item_subselect.h
index c6d1882a6b4..7f2aa857459 100644
--- a/sql/item_subselect.h
+++ b/sql/item_subselect.h
@@ -267,7 +267,7 @@ public:
   subs_type substype() { return SINGLEROW_SUBS; }
 
   void reset();
-  void no_rows_in_result() { reset(); make_const(); }
+  void no_rows_in_result();
   bool select_transformer(JOIN *join);
   void store(uint i, Item* item);
   double val_real();