Fixed #27718 -- Added QuerySet.union(), intersection(), difference().

Thanks Mariusz Felisiak for review and Oracle assistance.
Thanks Tim Graham for review and writing docs.

1 files changed, 55 insertions, 0 deletions

diff --git a/docs/ref/models/querysets.txt b/docs/ref/models/querysets.txt
index 5fe783514d..f5f0fbcc8b 100644
--- a/docs/ref/models/querysets.txt
+++ b/docs/ref/models/querysets.txt
@@ -801,6 +801,61 @@ typically caches its results. If the data in the database might have changed
 since a ``QuerySet`` was evaluated, you can get updated results for the same
 query by calling ``all()`` on a previously evaluated ``QuerySet``.
 
+``union()``
+~~~~~~~~~~~
+
+.. method:: union(*other_qs, all=False)
+
+.. versionadded:: 1.11
+
+Uses SQL's ``UNION`` operator to combine the results of two or more
+``QuerySet``\s. For example:
+
+    >>> qs1.union(qs2, qs3)
+
+The ``UNION`` operator selects only distinct values by default. To allow
+duplicate values, use the ``all=True`` argument.
+
+``union()``, ``intersection()``, and ``difference()`` return model instances
+of the type of the first ``QuerySet`` even if the arguments are ``QuerySet``\s
+of other models. Passing different models works as long as the ``SELECT`` list
+is the same in all ``QuerySet``\s (at least the types, the names don't matter
+as long as the types in the same order).
+
+In addition, only ``LIMIT``, ``OFFSET``, and ``ORDER BY`` (i.e. slicing and
+:meth:`order_by`) are allowed on the resulting ``QuerySet``. Further, databases
+place restrictions on what operations are allowed in the combined queries. For
+example, most databases don't allow ``LIMIT`` or ``OFFSET`` in the combined
+queries.
+
+``intersection()``
+~~~~~~~~~~~~~~~~~~
+
+.. method:: intersection(*other_qs)
+
+.. versionadded:: 1.11
+
+Uses SQL's ``INTERSECT`` operator to return the shared elements of two or more
+``QuerySet``\s. For example:
+
+    >>> qs1.itersect(qs2, qs3)
+
+See :meth:`union` for some restrictions.
+
+``difference()``
+~~~~~~~~~~~~~~~~
+
+.. method:: difference(*other_qs)
+
+.. versionadded:: 1.11
+
+Uses SQL's ``EXCEPT`` operator to keep only elements present in the
+``QuerySet`` but not in some other ``QuerySet``\s. For example::
+
+    >>> qs1.difference(qs2, qs3)
+
+See :meth:`union` for some restrictions.
+
 ``select_related()``
 ~~~~~~~~~~~~~~~~~~~~