Fixed #34262 -- Added support for AnyValue for SQLite, MySQL, Oracle, and Postgresql 16+.

Thanks Simon Charette for the guidance and review. Thanks Tim Schilling for the
documentation review. Thanks David Wobrock for investigation and solution proposals.

Author: ontowhee

django/db/backends/base/features.py

@@ -266,6 +266,9 @@ class BaseDatabaseFeatures:
     # delimiter along with DISTINCT.
     supports_aggregate_distinct_multiple_argument = True
 
+    # Does the database support SQL 2023 ANY_VALUE in GROUP BY?
+    supports_any_value = False
+
     # Does the backend support indexing a TextField?
     supports_index_on_text_field = True
 

django/db/backends/mysql/features.py

@@ -111,16 +111,6 @@ def django_test_skips(self):
                     },
                 }
             )
-        if "ONLY_FULL_GROUP_BY" in self.connection.sql_mode:
-            skips.update(
-                {
-                    "GROUP BY cannot contain nonaggregated column when "
-                    "ONLY_FULL_GROUP_BY mode is enabled on MySQL, see #34262.": {
-                        "aggregation.tests.AggregateTestCase."
-                        "test_group_by_nested_expression_with_params",
-                    },
-                }
-            )
         if self.connection.mysql_version < (8, 0, 31):
             skips.update(
                 {
@@ -297,3 +287,7 @@ def allows_group_by_selected_pks(self):
         if self.connection.mysql_is_mariadb:
             return "ONLY_FULL_GROUP_BY" not in self.connection.sql_mode
         return True
+
+    @cached_property
+    def supports_any_value(self):
+        return not self.connection.mysql_is_mariadb

django/db/backends/oracle/features.py

@@ -61,6 +61,7 @@ class DatabaseFeatures(BaseDatabaseFeatures):
         END;
     """
     supports_callproc_kwargs = True
+    supports_any_value = True
     supports_over_clause = True
     supports_frame_range_fixed_distance = True
     supports_ignore_conflicts = False

django/db/backends/postgresql/features.py

@@ -162,3 +162,5 @@ def is_postgresql_17(self):
     supports_nulls_distinct_unique_constraints = property(
         operator.attrgetter("is_postgresql_15")
     )
+
+    supports_any_value = property(operator.attrgetter("is_postgresql_16"))

django/db/backends/sqlite3/_functions.py

@@ -80,6 +80,7 @@ def register(connection):
     connection.create_aggregate("STDDEV_SAMP", 1, StdDevSamp)
     connection.create_aggregate("VAR_POP", 1, VarPop)
     connection.create_aggregate("VAR_SAMP", 1, VarSamp)
+    connection.create_aggregate("ANY_VALUE", 1, AnyValue)
     # Some math functions are enabled by default in SQLite 3.35+.
     sql = "select sqlite_compileoption_used('ENABLE_MATH_FUNCTIONS')"
     if not connection.execute(sql).fetchone()[0]:
@@ -513,3 +514,8 @@ class VarPop(ListAggregate):
 
 class VarSamp(ListAggregate):
     finalize = statistics.variance
+
+
+class AnyValue(ListAggregate):
+    def finalize(self):
+        return self[0]

django/db/backends/sqlite3/features.py

@@ -36,6 +36,7 @@ class DatabaseFeatures(BaseDatabaseFeatures):
     supports_aggregate_filter_clause = True
     supports_aggregate_order_by_clause = Database.sqlite_version_info >= (3, 44, 0)
     supports_aggregate_distinct_multiple_argument = False
+    supports_any_value = True
     order_by_nulls_first = True
     supports_json_field_contains = False
     supports_update_conflicts = True

django/db/models/aggregates.py

@@ -22,6 +22,7 @@
 
 __all__ = [
     "Aggregate",
+    "AnyValue",
     "Avg",
     "Count",
     "Max",
@@ -229,6 +230,20 @@ def _get_repr_options(self):
         return options
 
 
+class AnyValue(Aggregate):
+    function = "ANY_VALUE"
+    name = "AnyValue"
+    arity = 1
+    window_compatible = False
+
+    def as_sql(self, compiler, connection, **extra_context):
+        if not connection.features.supports_any_value:
+            raise NotSupportedError(
+                "ANY_VALUE is not supported on this database backend."
+            )
+        return super().as_sql(compiler, connection, **extra_context)
+
+
 class Avg(FixDurationInputMixin, NumericOutputFieldMixin, Aggregate):
     function = "AVG"
     name = "Avg"

docs/ref/models/querysets.txt

@@ -3943,6 +3943,60 @@ when the queryset (or grouping) contains no entries.
 Keyword arguments that can provide extra context for the SQL generated
 by the aggregate.
 
+``AnyValue``
+~~~~~~~~~~~~
+
+.. versionadded:: 6.0
+
+.. class:: AnyValue(expression, output_field=None, filter=None, default=None, **extra)
+
+    Returns an arbitrary value from the non-null input values.
+
+    * Default alias: ``<field>__anyvalue``
+    * Return type: same as input field, or ``output_field`` if supplied. If the
+      queryset or grouping is empty, ``default`` is returned.
+
+    Usage example:
+
+    .. code-block:: pycon
+
+        >>> # Get average rating for each year along with a sample headline
+        >>> # from that year.
+        >>> from django.db.models import AnyValue, Avg, F, Q
+        >>> sample_headline = AnyValue("headline")
+        >>> Entry.objects.values(
+        ...     pub_year=F("pub_date__year"),
+        ... ).annotate(
+        ...     avg_rating=Avg("rating"),
+        ...     sample_headline=sample_headline,
+        ... )
+
+        >>> # Get a sample headline from each year with rating greater than 4.5.
+        >>> sample_headline = AnyValue(
+        ...     "headline",
+        ...     filter=Q(rating__gt=4.5),
+        ... )
+        >>> Entry.objects.values(
+        ...     pub_year=F("pub_date__year"),
+        ... ).annotate(
+        ...     avg_rating=Avg("rating"),
+        ...     sample_headline=sample_headline,
+        ... )
+
+    Supported on SQLite, MySQL, Oracle, and PostgreSQL 16+.
+
+    .. admonition:: MySQL with ``ONLY_FULL_GROUP_BY`` enabled
+
+        When the ``ONLY_FULL_GROUP_BY`` SQL mode is enabled on MySQL it may be
+        necessary to use ``AnyValue`` if an aggregation includes a mix of
+        aggregate and non-aggregate functions. Using ``AnyValue`` allows the
+        non-aggregate function to be referenced in the select list when
+        database cannot determine that it is functionally dependent on the
+        columns in the `group by`_ clause. See the :ref:`aggregation
+        documentation <aggregation-mysql-only-full-group-by>` for more details.
+
+        .. _group by: https://dev.mysql.com/doc/refman/8.4/en/group-by-handling.html
+
 ``Avg``
 ~~~~~~~
 

docs/releases/6.0.txt

@@ -212,6 +212,10 @@ Models
 * :class:`~django.db.models.JSONField` now supports
   :ref:`negative array indexing <key-index-and-path-transforms>` on SQLite.
 
+* The new :class:`~django.db.models.AnyValue` aggregate returns an arbitrary
+  value from the non-null input values. This is supported on SQLite, MySQL,
+  Oracle, and PostgreSQL 16+.
+
 Pagination
 ~~~~~~~~~~
 

docs/topics/db/aggregation.txt

@@ -679,3 +679,65 @@ no books can be found:
 Under the hood, the :ref:`default <aggregate-default>` argument is implemented
 by wrapping the aggregate function with
 :class:`~django.db.models.functions.Coalesce`.
+
+.. _aggregation-mysql-only-full-group-by:
+
+Aggregating with MySQL ``ONLY_FULL_GROUP_BY`` enabled
+-----------------------------------------------------
+
+When using the ``values()`` clause to group query results for annotations in
+MySQL with the ``ONLY_FULL_GROUP_BY`` SQL mode enabled, you may need to apply
+:class:`~django.db.models.AnyValue` if the annotation includes a mix of
+aggregate and non-aggregate expressions.
+
+Take the following example:
+
+.. code-block:: pycon
+
+    >>> from django.db.models import F, Count, Greatest
+    >>> Book.objects.values(greatest_pages=Greatest("pages", 600)).annotate(
+    ...     num_authors=Count("authors"),
+    ...     pages_per_author=F("greatest_pages") / F("num_authors"),
+    ... ).aggregate(Avg("pages_per_author"))
+
+This creates groups of books based on the SQL column ``GREATEST(pages, 600)``.
+One unique group consists of books with 600 pages or less, and other unique
+groups will consist of books with the same pages. The ``pages_per_author``
+annotation is composed of aggregate and non-aggregate expressions,
+``num_authors`` is an aggregate expression while ``greatest_page`` isn't.
+
+Since the grouping is based on the ``greatest_pages`` expression, MySQL may be
+unable to determine that ``greatest_pages`` (used in the ``pages_per_author``
+expression) is functionally dependent on the grouped column. As a result, it
+may raise an error like:
+
+.. code-block:: pytb
+
+    OperationalError: (1055, "Expression #2 of SELECT list is not in GROUP BY
+    clause and contains nonaggregated column 'book_book.pages' which is not
+    functionally dependent on columns in GROUP BY clause; this is incompatible
+    with sql_mode=only_full_group_by")
+
+To avoid this, you can wrap the non-aggregate expression with
+:class:`~django.db.models.AnyValue`.
+
+.. code-block:: pycon
+
+    >>> from django.db.models import F, Count, Greatest
+    >>> Book.objects.values(
+    ...     greatest_pages=Greatest("pages", 600),
+    ... ).annotate(
+    ...     num_authors=Count("authors"),
+    ...     pages_per_author=AnyValue(F("greatest_pages")) / F("num_authors"),
+    ... ).aggregate(Avg("pages_per_author"))
+    {'pages_per_author__avg': 532.57143333}
+
+Other supported databases do not encounter the ``OperationalError`` in the
+example above because they can detect the functional dependency. In general,
+``AnyValue`` is useful when dealing with select list columns that involve
+non-aggregate functions or complex expressions not recognized by the database
+as functionally dependent on the columns in the grouping clause.
+
+.. versionchanged:: 6.0
+
+    The :class:`~django.db.models.AnyValue` aggregate was added.

tests/aggregation/tests.py

@@ -6,6 +6,7 @@
 from django.core.exceptions import FieldError
 from django.db import NotSupportedError, connection
 from django.db.models import (
+    AnyValue,
     Avg,
     Case,
     CharField,
@@ -1662,19 +1663,77 @@ def test_group_by_exists_annotation(self):
         self.assertEqual(dict(has_long_books_breakdown), {True: 2, False: 3})
 
     def test_group_by_nested_expression_with_params(self):
+        greatest_pages_param = "greatest_pages"
+        if connection.vendor == "mysql" and connection.features.supports_any_value:
+            greatest_pages_param = AnyValue("greatest_pages")
+
         books_qs = (
             Book.objects.annotate(greatest_pages=Greatest("pages", Value(600)))
             .values(
                 "greatest_pages",
             )
             .annotate(
                 min_pages=Min("pages"),
-                least=Least("min_pages", "greatest_pages"),
+                least=Least("min_pages", greatest_pages_param),
             )
             .values_list("least", flat=True)
         )
         self.assertCountEqual(books_qs, [300, 946, 1132])
 
+    @skipUnlessDBFeature("supports_any_value")
+    def test_any_value(self):
+        books_qs = (
+            Book.objects.values(greatest_pages=Greatest("pages", 600))
+            .annotate(
+                pubdate_year=AnyValue("pubdate__year"),
+            )
+            .values_list("pubdate_year", flat=True)
+            .order_by("pubdate_year")
+        )
+        self.assertCountEqual(books_qs[0:2], [1991, 1995])
+        self.assertIn(books_qs[2], [2007, 2008])
+
+    @skipUnlessDBFeature("supports_any_value")
+    def test_any_value_filter(self):
+        books_qs = (
+            Book.objects.values(greatest_pages=Greatest("pages", 600))
+            .annotate(
+                pubdate_year=AnyValue("pubdate__year", filter=Q(rating__lte=4.5)),
+            )
+            .values_list("pubdate_year", flat=True)
+        )
+        self.assertCountEqual(books_qs, [2007, 1995, None])
+
+    @skipUnlessDBFeature("supports_any_value")
+    def test_any_value_aggregate_clause(self):
+        books_qs = (
+            Book.objects.values(greatest_pages=Greatest("pages", 600))
+            .annotate(
+                num_authors=Count("authors"),
+                pages_per_author=(
+                    AnyValue("greatest_pages") / (Cast("num_authors", FloatField()))
+                ),
+            )
+            .values_list("pages_per_author", flat=True)
+            .order_by("pages_per_author")
+        )
+        self.assertAlmostEqual(books_qs[0], 600 / 7, places=4)
+        self.assertAlmostEqual(books_qs[1], 1132 / 2, places=4)
+        self.assertAlmostEqual(books_qs[2], 946 / 1, places=4)
+
+        aggregate_qs = books_qs.aggregate(Avg("pages_per_author"))
+        self.assertAlmostEqual(
+            aggregate_qs["pages_per_author__avg"],
+            ((600 / 7) + (1132 / 2) + (946 / 1)) / 3,
+            places=4,
+        )
+
+    @skipIfDBFeature("supports_any_value")
+    def test_any_value_not_supported(self):
+        message = "ANY_VALUE is not supported on this database backend."
+        with self.assertRaisesMessage(NotSupportedError, message):
+            Book.objects.aggregate(AnyValue("rating"))
+
     @skipUnlessDBFeature("supports_subqueries_in_group_by")
     def test_aggregation_subquery_annotation_related_field(self):
         publisher = Publisher.objects.create(name=self.a9.name, num_awards=2)