Fixed #28211 -- Prevented ORing an empty Q() from reducing query join efficiency.

1 files changed, 9 insertions, 0 deletions

diff --git a/django/db/models/query_utils.py b/django/db/models/query_utils.py
index 27430ae4ca..0fedfac3e2 100644
--- a/django/db/models/query_utils.py
+++ b/django/db/models/query_utils.py
@@ -5,6 +5,7 @@ Factored out from django.db.models.query to avoid making the main module very
 large and/or so that they can be used by other modules without getting into
 circular import difficulties.
 """
+import copy
 import functools
 import inspect
 from collections import namedtuple
@@ -61,6 +62,14 @@ class Q(tree.Node):
     def _combine(self, other, conn):
         if not isinstance(other, Q):
             raise TypeError(other)
+
+        # If the other Q() is empty, ignore it and just use `self`.
+        if not other:
+            return copy.deepcopy(self)
+        # Or if this Q is empty, ignore it and just use `other`.
+        elif not self:
+            return copy.deepcopy(other)
+
         obj = type(self)()
         obj.connector = conn
         obj.add(self, conn)