Bug#43668: Wrong comparison and MIN/MAX for YEAR(2)

MySQL manual describes values of the YEAR(2) field type as follows:
values 00 - 69 mean 2000 - 2069 years and values 70 - 99 mean 1970 - 1999
years. MIN/MAX and comparison functions was comparing them as int values
thus producing wrong result.

Now the Arg_comparator class is extended with compare_year function which
performs correct comparison of the YEAR type.
The Item_sum_hybrid class now uses Item_cache and Arg_comparator objects to
correctly calculate its value.
To allow Arg_comparator to use func_name() function for Item_func and Item_sum
objects the func_name declaration is moved to the Item_result_field class.
A helper function is_owner_equal_func is added to the Arg_comparator class.
It checks whether the Arg_comparator object owner is the <=> function or not.
A helper function setup is added to the Item_sum_hybrid class. It sets up
cache item and comparator.

1 files changed, 1 insertions, 0 deletions

diff --git a/sql/item_subselect.h b/sql/item_subselect.h
index d4aa621c083..467e9b22637 100644
--- a/sql/item_subselect.h
+++ b/sql/item_subselect.h
@@ -132,6 +132,7 @@ public:
     @return the SELECT_LEX structure associated with this Item
   */
   st_select_lex* get_select_lex();
+  const char *func_name() const { DBUG_ASSERT(0); return "subselect"; }
 
   friend class select_subselect;
   friend class Item_in_optimizer;