id	summary	reporter	owner	description	type	status	component	version	severity	resolution	keywords	cc	stage	has_patch	needs_docs	needs_tests	needs_better_patch	easy	ui_ux
37473	QuerySet.aggregate() crashes when values() selects only an aggregate annotation	cheek-walnut		"When `values()` selects only an aggregate annotation, a following `aggregate()` over another field generates a subquery with an empty SELECT list.

{{{#!python
class Author(models.Model):
    name = models.CharField(max_length=20)
    age = models.IntegerField()

class Book(models.Model):
    title = models.CharField(max_length=20)
    pages = models.IntegerField()
    author = models.ForeignKey(Author, models.CASCADE, related_name=""books"")
}}}

With two authors (ages 40 and 30) and one book each:

{{{
>>> Author.objects.annotate(c=Count(""books"")).values(""c"").aggregate(m=Max(""age""))
Traceback (most recent call last):
  ...
  File ""django/db/backends/sqlite3/base.py"", line 365, in execute
    return super().execute(query, params)
django.db.utils.OperationalError: near ""FROM"": syntax error
}}}

Generated SQL (SQLite):

{{{
SELECT MAX(""__col1"") FROM (SELECT  FROM ""app_author"" LEFT OUTER JOIN ""app_book"" ON (""app_author"".""id"" = ""app_book"".""author_id"") GROUP BY ""app_author"".""id"", ""app_author"".""name"", ""app_author"".""age"") subquery
}}}

Expected `{'m': 40}`, as on Django 5.1, where the inner query selects `""app_author"".""age"" AS ""__col1""`. `values_list(""c"")` fails the same way; `values(""name"", ""c"")` and `aggregate(m=Max(""c""))` work.

Regression in 65ad4ade74dc9208b9d686a451cd6045df0c9c3a (Refs #28900): the query works on its parent and fails on it. Reproduced on 5.2.20, 6.0.11, 6.1.4 and main (5bd95c57a2) with SQLite; 5.1.16 is not affected.

The cause appears to be `if self.selected:` in `Query.set_annotation_mask()` (django/db/models/sql/query.py:2568) and `Query.add_annotation()` (:1248), which treats an empty `selected` dict like `None`: after `get_aggregation()` masks the unused `c` annotation, `selected` is `{}` and the `__col1` column added for the aggregate is never added to it.

AI disclosure: found during a code audit with Claude Code 2.1.317 (Claude Opus 5.5), which also reduced the test case and ran it on the versions above and on 65ad4ade74 and its parent. I reviewed this report and re-ran the reproduction on main and 5.1.16."	Bug	new	Database layer (models, ORM)	5.2	Low				Unreviewed	0	0	0	0	0	0