A fix and test case for Bug#6297 "prepared statement, wrong handling

 of <parameter> IS NULL":
we must not only set Item::null_value in Item_param, but implement
Item_param::is_null() to work well with IS NULL/IS NOT NULL clauses.


mysql-test/r/ps.result:
  Test case for Bug#6297: test results fixed.
mysql-test/t/ps.test:
  A test case for Bug#6297 "prepared statement, wrong handling of 
  <parameter> IS NULL"
sql/item.h:
  A fix for Bug#6297: we must not only set null_value in Item_param, but
  also implement Item_param::is_null() to work well with  IS NULL/
  IS NOT NULL.
  Item::is_null() commented.

1 files changed, 10 insertions, 0 deletions

diff --git a/sql/item.h b/sql/item.h
index 547577a7ee0..ccb0fda1c49 100644
--- a/sql/item.h
+++ b/sql/item.h
@@ -266,6 +266,14 @@ public:
   virtual bool get_time(TIME *ltime);
   virtual bool get_date_result(TIME *ltime,uint fuzzydate)
   { return get_date(ltime,fuzzydate); }
+  /*
+    This function is used only in Item_func_isnull/Item_func_isnotnull
+    (implementations of IS NULL/IS NOT NULL clauses). Item_func_is{not}null
+    calls this method instead of one of val/result*() methods, which
+    normally will set null_value. This allows to determine nullness of
+    a complex expression without fully evaluating it.
+    Any new item which can be NULL must implement this call.
+  */
   virtual bool is_null() { return 0; }
   /*
     it is "top level" item of WHERE clause and we do not need correct NULL
@@ -573,6 +581,8 @@ public:
   void print(String *str) { str->append('?'); }
   /* parameter never equal to other parameter of other item */
   bool eq(const Item *item, bool binary_cmp) const { return 0; }
+  bool is_null()
+  { DBUG_ASSERT(state != NO_VALUE); return state == NULL_VALUE; }
 };
 
 class Item_int :public Item_num