Revert 59685, as we now cache datetimes correctly.

See also bug 11775312, all queries listed there now have the
same results here, as they have in 5.1

mysql-test/r/type_date.result

@@ -303,10 +303,10 @@ CREATE TABLE t1(a DATE, b YEAR, KEY(a));
 INSERT INTO t1 VALUES ('2011-01-01',2011);
 SELECT b = (SELECT CONVERT(a, DATE) FROM t1 GROUP BY a) FROM t1;
 b = (SELECT CONVERT(a, DATE) FROM t1 GROUP BY a)
-0
+1
 SELECT b = CONVERT((SELECT CONVERT(a, DATE) FROM t1 GROUP BY a), DATE) FROM t1;
 b = CONVERT((SELECT CONVERT(a, DATE) FROM t1 GROUP BY a), DATE)
-0
+1
 DROP TABLE t1;
 End of 5.1 tests
 #

sql/item_cmpfunc.cc

@@ -403,8 +403,7 @@ static bool convert_constant_item(THD *thd, Item_field *field_item,
   Field *field= field_item->field;
   int result= 0;
 
-  // TODO: revert Bug#59685 here, as we now cache datetimes correctly.
-  if (!(*item)->with_subselect && (*item)->const_item())
+  if ((*item)->const_item())
   {
     TABLE *table= field->table;
     ulonglong orig_sql_mode= thd->variables.sql_mode;