[1.11.x] Fixed #28399 -- Fixed QuerySet.count() for union(), difference(), and intersection() queries.

Backport of adab280cefb15659c39558ac26ea392b0a1e456c from master

2 files changed, 6 insertions, 6 deletions

diff --git a/django/db/models/sql/compiler.py b/django/db/models/sql/compiler.py
index e96cbee71f..6ec2284a91 100644
--- a/django/db/models/sql/compiler.py
+++ b/django/db/models/sql/compiler.py
@@ -398,7 +398,7 @@ class SQLCompiler(object):
                     continue
                 raise
         if not parts:
-            return [], []
+            raise EmptyResultSet
         combinator_sql = self.connection.ops.set_operators[combinator]
         if all and combinator == 'union':
             combinator_sql += ' ALL'
diff --git a/django/db/models/sql/query.py b/django/db/models/sql/query.py
index e2d273994e..d1c4e5446b 100644
--- a/django/db/models/sql/query.py
+++ b/django/db/models/sql/query.py
@@ -416,12 +416,12 @@ class Query(object):
         # aren't smart enough to remove the existing annotations from the
         # query, so those would force us to use GROUP BY.
         #
-        # If the query has limit or distinct, then those operations must be
-        # done in a subquery so that we are aggregating on the limit and/or
-        # distinct results instead of applying the distinct and limit after the
-        # aggregation.
+        # If the query has limit or distinct, or uses set operations, then
+        # those operations must be done in a subquery so that the query
+        # aggregates on the limit and/or distinct results instead of applying
+        # the distinct and limit after the aggregation.
         if (isinstance(self.group_by, list) or has_limit or has_existing_annotations or
-                self.distinct):
+                self.distinct or self.combinator):
             from django.db.models.sql.subqueries import AggregateQuery
             outer_query = AggregateQuery(self.model)
             inner_query = self.clone()