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[5.0.x] Refs #34808 -- Doc'd that aggregation functions on empty groups can return None.

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David Sanders 2023-09-20 23:58:23 +10:00 committed by Natalia
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docs/ref/models/querysets.txt
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@ -3845,14 +3845,15 @@ documentation to learn how to create your aggregates.
currently emulates these features using a text field. Attempts to use currently emulates these features using a text field. Attempts to use
aggregation on date/time fields in SQLite will raise ``NotSupportedError``. aggregation on date/time fields in SQLite will raise ``NotSupportedError``.
.. admonition:: Empty queryset .. admonition:: Empty querysets or groups
Aggregation functions return ``None`` when used with an empty Aggregation functions return ``None`` when used with an empty ``QuerySet``
``QuerySet``. For example, the ``Sum`` aggregation function returns ``None`` or group. For example, the ``Sum`` aggregation function returns ``None``
instead of ``0`` if the ``QuerySet`` contains no entries. To return another instead of ``0`` if the ``QuerySet`` contains no entries or for any empty
value instead, pass a value to the ``default`` argument. An exception is group in a non-empty ``QuerySet``. To return another value instead, define
``Count``, which does return ``0`` if the ``QuerySet`` is empty. ``Count`` the ``default`` argument. ``Count`` is an exception to this behavior; it
does not support the ``default`` argument. returns ``0`` if the ``QuerySet`` is empty since ``Count`` does not support
the ``default`` argument.
All aggregates have the following parameters in common: All aggregates have the following parameters in common: