Django/django
11
0
Fork 0
Code Pull Requests Projects Releases Activity

[1.9.x] Refs #10060 -- Corrected description of multiple annotations bug.

Browse Source 
Backport of 3d2236773ba88e330841b8c72183b0e978e10909 from master
This commit is contained in:
Tim Graham 2015-12-08 16:45:15 -05:00
parent 192d1eb5c3
commit ea63cf8d42
1 changed files with 4 additions and 5 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

9
docs/topics/db/aggregation.txt
View File

@ -190,9 +190,8 @@ Combining multiple aggregations
------------------------------- -------------------------------
Combining multiple aggregations with ``annotate()`` will `yield the wrong Combining multiple aggregations with ``annotate()`` will `yield the wrong
results <https://code.djangoproject.com/ticket/10060>`_, as multiple tables are results <https://code.djangoproject.com/ticket/10060>`_ because joins are used
cross joined. Due to the use of ``LEFT OUTER JOIN``, duplicate records will be instead of subqueries:
generated if some of the joined tables contain more records than the others:
>>> Book.objects.first().authors.count() >>> Book.objects.first().authors.count()
2 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. rating exceeding 3.0, hence publisher C is excluded.
In the first query, the annotation precedes the filter, so the filter has no 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 effect on the annotation. ``distinct=True`` is required to avoid a :ref:`query
:ref:`cross-join bug <combining-multiple-aggregations>`. bug <combining-multiple-aggregations>`.
The second query counts the number of books that have a rating exceeding 3.0 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 for each publisher. The filter precedes the annotation, so the filter