[1.6.x] Documented a current limitation of multiple table annotation; refs #10060.

Backport of 4b23a6c7a9232cc07ec95fe98be17efbd4449822 from master

1 files changed, 11 insertions, 0 deletions

diff --git a/docs/topics/db/aggregation.txt b/docs/topics/db/aggregation.txt
index 1024d6b0c2..90735c31a4 100644
--- a/docs/topics/db/aggregation.txt
+++ b/docs/topics/db/aggregation.txt
@@ -179,6 +179,17 @@ of the ``annotate()`` clause is a ``QuerySet``; this ``QuerySet`` can be
 modified using any other ``QuerySet`` operation, including ``filter()``,
 ``order_by()``, or even additional calls to ``annotate()``.
 
+.. admonition:: If in doubt, inspect the SQL query!
+
+    In order to understand what happens in your query, consider inspecting the
+    ``query`` property of your ``QuerySet``.
+
+    For instance, combining multiple aggregations with ``annotate()`` will
+    yield the wrong results, as `multiple tables are the cross joined`_,
+    resulting in duplicate row aggregations.
+
+.. _multiple tables are the cross joined: https://code.djangoproject.com/ticket/10060
+
 Joins and aggregates
 ====================