MDEV-4265 5.5 is slower than 5.3 because of many str_to_datetime calls

get_datetime_value() should not double-cache its own Item_cache_temporal items,
but it *should* cache other Item_cache items, such as Item_cache_str.

sql/item.h:
  shortcut, to avoid going through the switch in Item::cmp_type()
sql/item_cmpfunc.cc:
  even if the item is Item_cache_str - it still needs to be converted and cached.
sql/item_timefunc.h:
  all descendants of Item_temporal_func always have cmp_type==TIME_RESULT.
  Even Item_date_add_interval, that might have field_type == MYSQL_TYPE_STRING.

1 files changed, 1 insertions, 0 deletions

diff --git a/sql/item_timefunc.h b/sql/item_timefunc.h
index 3e3cd698efc..9b2db9e816e 100644
--- a/sql/item_timefunc.h
+++ b/sql/item_timefunc.h
@@ -491,6 +491,7 @@ public:
   enum Item_result result_type () const { return STRING_RESULT; }
   CHARSET_INFO *charset_for_protocol(void) const { return &my_charset_bin; }
   enum_field_types field_type() const { return MYSQL_TYPE_DATETIME; }
+  Item_result cmp_type() const { return TIME_RESULT; }
   String *val_str(String *str);
   longlong val_int();
   double val_real();