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Code Issues Releases Wiki Activity

Refs #10060 -- Corrected description of multiple annotations bug.

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This commit is contained in:
Tim Graham 2015-12-08 16:45:15 -05:00
parent 69b69f6d60
commit 3d2236773b
1 changed files with 4 additions and 5 deletions
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9
docs/topics/db/aggregation.txt
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@ -190,9 +190,8 @@ Combining multiple aggregations
-------------------------------
Combining multiple aggregations with ``annotate()`` will `yield the wrong
results <https://code.djangoproject.com/ticket/10060>`_, as multiple tables are
cross joined. Due to the use of ``LEFT OUTER JOIN``, duplicate records will be
generated if some of the joined tables contain more records than the others:
results <https://code.djangoproject.com/ticket/10060>`_ because joins are used
instead of subqueries:
>>> Book.objects.first().authors.count()
2
@ -374,8 +373,8 @@ Both queries return a list of publishers that have at least one book with a
rating exceeding 3.0, hence publisher C is excluded.
In the first query, the annotation precedes the filter, so the filter has no
effect on the annotation. ``distinct=True`` is required to avoid a
:ref:`cross-join bug <combining-multiple-aggregations>`.
effect on the annotation. ``distinct=True`` is required to avoid a :ref:`query
bug <combining-multiple-aggregations>`.
The second query counts the number of books that have a rating exceeding 3.0
for each publisher. The filter precedes the annotation, so the filter