Made some types of nested update queries very slightly more efficient at the

database level. Also worked around the fact that MySQL (and maybe other
backends we don't know about) cannot select from the table they're updating.

Fixed #7095.


git-svn-id: http://code.djangoproject.com/svn/django/trunk@7496 bcc190cf-cafb-0310-a4f2-bffc1f526a37

django/db/backends/mysql/base.py

@@ -63,6 +63,7 @@ class DatabaseFeatures(BaseDatabaseFeatures):
     autoindexes_primary_keys = False
     inline_fk_references = False
     empty_fetchmany_value = ()
+    update_can_self_select = False
 
 class DatabaseOperations(BaseDatabaseOperations):
     def date_extract_sql(self, lookup_type, field_name):