Refs #28643 -- Changed Variance() to use NumericOutputFieldMixin.

Keeps precision instead of forcing DecimalField to FloatField.

django/db/models/aggregates.py

@@ -3,7 +3,7 @@ Classes to represent the definitions of aggregate functions.
 """
 from django.core.exceptions import FieldError
 from django.db.models.expressions import Case, Func, Star, When
-from django.db.models.fields import FloatField, IntegerField
+from django.db.models.fields import IntegerField
 from django.db.models.functions.mixins import NumericOutputFieldMixin
 
 __all__ = [
@@ -172,9 +172,8 @@ class Sum(Aggregate):
         return super().as_sql(compiler, connection, **extra_context)
 
 
-class Variance(Aggregate):
+class Variance(NumericOutputFieldMixin, Aggregate):
     name = 'Variance'
-    output_field = FloatField()
 
     def __init__(self, expression, sample=False, **extra):
         self.function = 'VAR_SAMP' if sample else 'VAR_POP'

docs/ref/models/querysets.txt

@@ -3419,12 +3419,13 @@ by the aggregate.
 ``Variance``
 ~~~~~~~~~~~~
 
-.. class:: Variance(expression, sample=False, filter=None, **extra)
+.. class:: Variance(expression, output_field=None, sample=False, filter=None, **extra)
 
     Returns the variance of the data in the provided expression.
 
     * Default alias: ``<field>__variance``
-    * Return type: ``float``
+    * Return type: ``float`` if input is ``int``, otherwise same as input
+      field, or ``output_field`` if supplied
 
     Has one optional argument:
 

docs/releases/2.2.txt

@@ -493,9 +493,9 @@ Miscellaneous
 
 * :djadmin:`runserver` no longer supports `pyinotify` (replaced by Watchman).
 
-* The :class:`~django.db.models.Avg` and :class:`~django.db.models.StdDev`
-  aggregate functions now return a ``Decimal`` instead of a ``float`` when the
-  input is ``Decimal``.
+* The :class:`~django.db.models.Avg`, :class:`~django.db.models.StdDev`, and
+  :class:`~django.db.models.Variance` aggregate functions now return a
+  ``Decimal`` instead of a ``float`` when the input is ``Decimal``.
 
 .. _deprecated-features-2.2:
 

tests/aggregation_regress/tests.py

@@ -1160,7 +1160,7 @@ class AggregationTests(TestCase):
 
         self.assertEqual(
             Book.objects.aggregate(Variance('price')),
-            {'price__variance': Approximate(583.77, 1)}
+            {'price__variance': Approximate(Decimal('583.77'), 1)}
         )
 
         self.assertEqual(
@@ -1175,7 +1175,7 @@ class AggregationTests(TestCase):
 
         self.assertEqual(
             Book.objects.aggregate(Variance('price', sample=True)),
-            {'price__variance': Approximate(700.53, 2)}
+            {'price__variance': Approximate(Decimal('700.53'), 2)}
         )
 
     def test_filtering_by_annotation_name(self):