Refs #30188 -- Prevented double annotation of subquery when aggregated over.

Thanks Can Sarıgöl for the suggested trimming approach.

django/db/models/sql/query.py

@@ -383,12 +383,16 @@ class Query(BaseExpression):
                 new_expr, col_cnt = self.rewrite_cols(expr, col_cnt)
                 new_exprs.append(new_expr)
             elif isinstance(expr, (Col, Subquery)) or (expr.contains_aggregate and not expr.is_summary):
-                # Reference to column. Make sure the referenced column
-                # is selected.
-                col_cnt += 1
-                col_alias = '__col%d' % col_cnt
-                self.annotations[col_alias] = expr
-                self.append_annotation_mask([col_alias])
+                # Reference to column, subquery, or another aggregate. Make
+                # sure the expression is selected and reuse its alias if so.
+                for col_alias, selected_annotation in self.annotation_select.items():
+                    if selected_annotation == expr:
+                        break
+                else:
+                    col_cnt += 1
+                    col_alias = '__col%d' % col_cnt
+                    self.annotations[col_alias] = expr
+                    self.append_annotation_mask([col_alias])
                 new_exprs.append(Ref(col_alias, expr))
             else:
                 # Some other expression not referencing database values

tests/expressions/tests.py

@@ -553,16 +553,20 @@ class BasicExpressionsTests(TestCase):
 
     @skipUnlessDBFeature('supports_subqueries_in_group_by')
     def test_aggregate_subquery_annotation(self):
-        aggregate = Company.objects.annotate(
-            ceo_salary=Subquery(
-                Employee.objects.filter(
-                    id=OuterRef('ceo_id'),
-                ).values('salary')
-            ),
-        ).aggregate(
-            ceo_salary_gt_20=Count('pk', filter=Q(ceo_salary__gt=20)),
-        )
+        with self.assertNumQueries(1) as ctx:
+            aggregate = Company.objects.annotate(
+                ceo_salary=Subquery(
+                    Employee.objects.filter(
+                        id=OuterRef('ceo_id'),
+                    ).values('salary')
+                ),
+            ).aggregate(
+                ceo_salary_gt_20=Count('pk', filter=Q(ceo_salary__gt=20)),
+            )
         self.assertEqual(aggregate, {'ceo_salary_gt_20': 1})
+        # Aggregation over a subquery annotation doesn't annotate the subquery
+        # twice in the inner query.
+        self.assertLessEqual(ctx.captured_queries[0]['sql'].count('SELECT'), 4,)
 
     def test_explicit_output_field(self):
         class FuncA(Func):