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, 9 insertions, 1 deletions

diff --git a/sql/item_subselect.cc b/sql/item_subselect.cc
index 9d7edda8eb5..cae1a9f7541 100644
--- a/sql/item_subselect.cc
+++ b/sql/item_subselect.cc
@@ -892,13 +892,21 @@ void Item_maxmin_subselect::print(String *str, enum_query_type query_type)
 
 void Item_maxmin_subselect::no_rows_in_result()
 {
-  value= 0;
+  value= Item_cache::get_cache(new Item_null());
   null_value= 0;
   was_values= 0;
   make_const();
 }
 
 
+void Item_singlerow_subselect::no_rows_in_result()
+{
+  value= Item_cache::get_cache(new Item_null());
+  reset();
+  make_const();
+}
+
+
 void Item_singlerow_subselect::reset()
 {
   Item_subselect::reset();