Fix for LP#612894 Some aggregate functions (such as MIN MAX) work incorrectly in subqueries after getting NULL value

mysql-test/r/group_by.result:
  Added test that showed problems that no_rows_in_results() didn't work for expressions
mysql-test/r/subselect4.result:
  Test case for LP#612894
mysql-test/t/group_by.test:
  Added test that showed problems that no_rows_in_results() didn't work for expressions
mysql-test/t/subselect4.test:
  Test case for LP#612894
sql/item.h:
  Added restore_to_before_no_rows_in_result()
  Added function processor for no_rows_in_results() and restore_to_before_no_rows_in_results() to ensure it works with functions
  Fix that above functions are handled by Item_ref()
sql/item_func.h:
  Ensure that no_rows_in_results() and restore_to_before_no_rows_in_result() are called for all function arguments
sql/item_sum.cc:
  Added restore_to_before_no_rows_in_result() to restore settings after Item_sum_hybrid::no_rows_in_result() was called.
  This is needed to handle the case where we have made 'make_const()' on the item in opt_sum(), but the item will be reused again in a sub query.
  Ignore multiple calls to no_rows_in_result() as Item_ref is calling it twice.
sql/item_sum.h:
  Added restore_to_before_no_rows_in_result();
sql/sql_select.cc:
  Added reset of no_rows_in_result() for JOIN::reinit()
sql/sql_select.h:
  Added marker if no_rows_in_result() is called.

1 files changed, 16 insertions, 2 deletions

diff --git a/sql/item_sum.cc b/sql/item_sum.cc
index 2f79fd65ff3..b3b07119066 100644
--- a/sql/item_sum.cc
+++ b/sql/item_sum.cc
@@ -1638,8 +1638,22 @@ void Item_sum_hybrid::cleanup()
 
 void Item_sum_hybrid::no_rows_in_result()
 {
-  was_values= FALSE;
-  clear();
+  /* We may be called here twice in case of ref field in function */
+  if (was_values)
+  {
+    was_values= FALSE;
+    was_null_value= value->null_value;
+    clear();
+  }
+}
+
+void Item_sum_hybrid::restore_to_before_no_rows_in_result()
+{
+  if (!was_values)
+  {
+    was_values= TRUE;
+    null_value= value->null_value= was_null_value;
+  }
 }