Bug#28494: Grouping by Item_func_set_user_var produces incorrect result.

This is an additional fix.
Item::val_xxx methods are supposed to use original data source and
Item::val_xxx_result methods to use the item's result field. But for the
Item_func_set_user_var class val_xxx_result methods were mapped to val_xxx
methods. This leads, in particular, to producing bad sort keys and thus
wrong order of the result set of queries with group by/order by clauses.

The set of val_xxx_result methods is added to the Item_func_set_user_var
class. It's the same as the val_xxx set of method but uses the result_field
to return a value.


mysql-test/t/user_var.test:
  Corrected test case for hte bug#28494.
mysql-test/r/user_var.result:
  Corrected test case for hte bug#28494.
sql/item_func.cc:
  Bug#28494: Grouping by Item_func_set_user_var produces incorrect result.
  The set of val_xxx_result methods is added to the Item_func_set_user_var
  class. It's the same as the val_xxx set of method but uses the result_field
  to return a value.
sql/item_func.h:
  Bug#28494: Grouping by Item_func_set_user_var produces incorrect result.
  The set of val_xxx_result methods is added to the Item_func_set_user_var
  class.

1 files changed, 4 insertions, 0 deletions

diff --git a/sql/item_func.h b/sql/item_func.h
index 18cd87d2de4..c8ea79b9747 100644
--- a/sql/item_func.h
+++ b/sql/item_func.h
@@ -1208,6 +1208,10 @@ public:
   longlong val_int();
   String *val_str(String *str);
   my_decimal *val_decimal(my_decimal *);
+  double val_real_result();
+  longlong val_int_result();
+  String *val_str_result(String *str);
+  my_decimal *val_decimal_result(my_decimal *);
   bool update_hash(void *ptr, uint length, enum Item_result type,
   		   CHARSET_INFO *cs, Derivation dv, bool unsigned_arg);
   bool send(Protocol *protocol, String *str_arg);