Fixed #23797 -- Fixed QuerySet.exclude() when rhs is a nullable column.

AUTHORS

@@ -392,6 +392,7 @@ answer newbie questions, and generally made Django that much better:
     Jacob Burch <jacobburch@gmail.com>
     Jacob Green
     Jacob Kaplan-Moss <jacob@jacobian.org>
+    Jacob Walls <http://www.jacobtylerwalls.com/>
     Jakub Paczkowski <jakub@paczkowski.eu>
     Jakub Wilk <jwilk@jwilk.net>
     Jakub Wiśniowski <restless.being@gmail.com>

django/db/models/sql/query.py

@@ -1324,9 +1324,7 @@ class Query(BaseExpression):
         require_outer = lookup_type == 'isnull' and condition.rhs is True and not current_negated
         if current_negated and (lookup_type != 'isnull' or condition.rhs is False) and condition.rhs is not None:
             require_outer = True
-            if (lookup_type != 'isnull' and (
-                    self.is_nullable(targets[0]) or
-                    self.alias_map[join_list[-1]].join_type == LOUTER)):
+            if lookup_type != 'isnull':
                 # The condition added here will be SQL like this:
                 # NOT (col IS NOT NULL), where the first NOT is added in
                 # upper layers of code. The reason for addition is that if col
@@ -1336,9 +1334,18 @@ class Query(BaseExpression):
                 # (col IS NULL OR col != someval)
                 #   <=>
                 # NOT (col IS NOT NULL AND col = someval).
-                lookup_class = targets[0].get_lookup('isnull')
-                col = self._get_col(targets[0], join_info.targets[0], alias)
-                clause.add(lookup_class(col, False), AND)
+                if (
+                    self.is_nullable(targets[0]) or
+                    self.alias_map[join_list[-1]].join_type == LOUTER
+                ):
+                    lookup_class = targets[0].get_lookup('isnull')
+                    col = self._get_col(targets[0], join_info.targets[0], alias)
+                    clause.add(lookup_class(col, False), AND)
+                # If someval is a nullable column, someval IS NOT NULL is
+                # added.
+                if isinstance(value, Col) and self.is_nullable(value.target):
+                    lookup_class = value.target.get_lookup('isnull')
+                    clause.add(lookup_class(value, False), AND)
         return clause, used_joins if not require_outer else ()
 
     def add_filter(self, filter_clause):

tests/queries/models.py

@@ -142,6 +142,7 @@ class Cover(models.Model):
 class Number(models.Model):
     num = models.IntegerField()
     other_num = models.IntegerField(null=True)
+    another_num = models.IntegerField(null=True)
 
     def __str__(self):
         return str(self.num)

tests/queries/tests.py

@@ -2372,7 +2372,10 @@ class ValuesQuerysetTests(TestCase):
         qs = Number.objects.extra(select={'num2': 'num+1'}).annotate(Count('id'))
         values = qs.values_list(named=True).first()
         self.assertEqual(type(values).__name__, 'Row')
-        self.assertEqual(values._fields, ('num2', 'id', 'num', 'other_num', 'id__count'))
+        self.assertEqual(
+            values._fields,
+            ('num2', 'id', 'num', 'other_num', 'another_num', 'id__count'),
+        )
         self.assertEqual(values.num, 72)
         self.assertEqual(values.num2, 73)
         self.assertEqual(values.id__count, 1)
@@ -2855,6 +2858,18 @@ class ExcludeTests(TestCase):
         self.r1.delete()
         self.assertFalse(qs.exists())
 
+    def test_exclude_nullable_fields(self):
+        number = Number.objects.create(num=1, other_num=1)
+        Number.objects.create(num=2, other_num=2, another_num=2)
+        self.assertSequenceEqual(
+            Number.objects.exclude(other_num=F('another_num')),
+            [number],
+        )
+        self.assertSequenceEqual(
+            Number.objects.exclude(num=F('another_num')),
+            [number],
+        )
+
 
 class ExcludeTest17600(TestCase):
     """