Fix aggregate queries with case expressions (#354)

* Fix aggregate queries with case expressions

mssql/base.py

@@ -9,6 +9,8 @@
 import time
 import struct
 import datetime
+from decimal import Decimal
+from uuid import UUID
 
 from django.core.exceptions import ImproperlyConfigured
 from django.utils.functional import cached_property
@@ -571,6 +573,36 @@ def __init__(self, cursor, connection):
         self.last_sql = ''
         self.last_params = ()
 
+    def _as_sql_type(self, typ, value):
+        if isinstance(value, str):
+            length = len(value)
+            if length == 0:
+                return 'NVARCHAR'
+            elif length > 4000:
+                return 'NVARCHAR(max)'
+            return 'NVARCHAR(%s)' % len(value)
+        elif typ == int:
+            if value < 0x7FFFFFFF and value > -0x7FFFFFFF:
+                return 'INT'
+            else:
+                return 'BIGINT'
+        elif typ == float:
+            return 'DOUBLE PRECISION'
+        elif typ == bool:
+            return 'BIT'
+        elif isinstance(value, Decimal):
+            return 'NUMERIC'
+        elif isinstance(value, datetime.datetime):
+            return 'DATETIME2'
+        elif isinstance(value, datetime.date):
+            return 'DATE'
+        elif isinstance(value, datetime.time):
+            return 'TIME'
+        elif isinstance(value, UUID):
+            return 'uniqueidentifier'
+        else:
+            raise NotImplementedError('Not supported type %s (%s)' % (type(value), repr(value)))
+
     def close(self):
         if self.active:
             self.active = False
@@ -588,6 +620,27 @@ def format_sql(self, sql, params):
 
         return sql
 
+    def format_group_by_params(self, query, params):
+        if params:
+            # Insert None params directly into the query
+            if None in params:
+                null_params = ['NULL' if param is None else '%s' for param in params]
+                query = query % tuple(null_params)
+                params = tuple(p for p in params if p is not None)
+            params = [(param, type(param)) for param in params]
+            params_dict = {param: '@var%d' % i for i, param in enumerate(set(params))}
+            args = [params_dict[param] for param in params]
+
+            variables = []
+            params = []
+            for key, value in params_dict.items():
+                datatype = self._as_sql_type(key[1], key[0])
+                variables.append("%s %s = %%s " % (value, datatype))
+                params.append(key[0])
+            query = ('DECLARE %s \n' % ','.join(variables)) + (query % tuple(args))
+
+        return query, params
+
     def format_params(self, params):
         fp = []
         if params is not None:
@@ -616,6 +669,8 @@ def format_params(self, params):
 
     def execute(self, sql, params=None):
         self.last_sql = sql
+        if 'GROUP BY' in sql:
+            sql, params = self.format_group_by_params(sql, params)
         sql = self.format_sql(sql, params)
         params = self.format_params(params)
         self.last_params = params

testapp/settings.py

@@ -284,8 +284,6 @@
     'aggregation.test_filter_argument.FilteredAggregateTests.test_filtered_aggregate_ref_subquery_annotation',
     'aggregation.tests.AggregateAnnotationPruningTests.test_referenced_group_by_annotation_kept',
     'aggregation.tests.AggregateAnnotationPruningTests.test_referenced_window_requires_wrapping',
-    'aggregation.tests.AggregateAnnotationPruningTests.test_unused_aliased_aggregate_and_annotation_reverse_fk',
-    'aggregation.tests.AggregateAnnotationPruningTests.test_unused_aliased_aggregate_and_annotation_reverse_fk_grouped',
     'aggregation.tests.AggregateTestCase.test_group_by_nested_expression_with_params',
     'expressions.tests.BasicExpressionsTests.test_aggregate_subquery_annotation',
     'queries.test_qs_combinators.QuerySetSetOperationTests.test_union_order_with_null_first_last',

testapp/tests/test_expressions.py

@@ -5,12 +5,13 @@
 from unittest import skipUnless
 
 from django import VERSION
-from django.db.models import IntegerField, F
+from django.db.models import CharField, IntegerField, F
 from django.db.models.expressions import Case, Exists, OuterRef, Subquery, Value, When, ExpressionWrapper
 from django.test import TestCase, skipUnlessDBFeature
 
-from django.db.models.aggregates import Count
-from ..models import Author, Comment, Post, Editor, ModelWithNullableFieldsOfDifferentTypes
+from django.db.models.aggregates import Count, Sum
+
+from ..models import Author, Book, Comment, Post, Editor, ModelWithNullableFieldsOfDifferentTypes
 
 
 DJANGO3 = VERSION[0] >= 3
@@ -85,6 +86,14 @@ def test_order_by_exists(self):
         self.assertSequenceEqual(authors_by_posts, [author_without_posts, self.author])
 
 
+class TestGroupBy(TestCase):
+    def test_group_by_case(self):
+        annotated_queryset = Book.objects.annotate(age=Case(
+            When(id__gt=1000, then=Value("new")),
+            default=Value("old"),
+            output_field=CharField())).values('age').annotate(sum=Sum('id'))
+        self.assertEqual(list(annotated_queryset.all()), [])
+
 @skipUnless(DJANGO3, "Django 3 specific tests")
 @skipUnlessDBFeature("order_by_nulls_first")
 class TestOrderBy(TestCase):