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	count() and aggregate() build an empty SELECT when values() selects only aggregate annotations	cheek-walnut		"When `values()` selects only an aggregate annotation, a following `count()`, or `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 5.2.19, 6.0.10, 6.1.3 and main with SQLite; 5.1.15 is not affected. On PostgreSQL (checked on 16), which accepts an empty SELECT list, `count()` returns the right number but `aggregate(m=Max(""age""))` fails with `column ""__col1"" does not exist`.

The cause appears to be `if self.selected:` in `Query.set_annotation_mask()` (django/db/models/sql/query.py:2568 at 5bd95c57a2) 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. `count()` also goes through the fallback that selects the primary key when nothing else is selected (query.py:595-605), which only sets `inner_query.select` and is ignored once `selected` is `{}`, so changing the two checks to `is not None` fixes `aggregate()` but not `count()`.

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. The PostgreSQL behavior and the `count()` note came from an independent review with ChatGPT Pro and were re-run with Claude Code. I reviewed this report and re-ran the reproduction on main and stable/5.1.x."	Bug	new	Database layer (models, ORM)	5.2	Low				Unreviewed	0	0	0	0	0	0