Fixed #12192 -- Don't execute any DB query when the QS slicing being …

…performed

will result in use of LIMIT 0. Thanks Suor for the report.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@14204 bcc190cf-cafb-0310-a4f2-bffc1f526a37

django/db/backends/oracle/compiler.py

@@ -27,6 +27,8 @@ def as_sql(self, with_limits=True, with_col_aliases=False):
         If 'with_limits' is False, any limit/offset information is not
         included in the query.
         """
+        if with_limits and self.query.low_mark == self.query.high_mark:
+            return '', ()
 
         # The `do_offset` flag indicates whether we need to construct
         # the SQL needed to use limit/offset with Oracle.

django/db/models/sql/compiler.py

@@ -52,6 +52,9 @@ def as_sql(self, with_limits=True, with_col_aliases=False):
         If 'with_limits' is False, any limit/offset information is not included
         in the query.
         """
+        if with_limits and self.query.low_mark == self.query.high_mark:
+            return '', ()
+
         self.pre_sql_setup()
         out_cols = self.get_columns(with_col_aliases)
         ordering, ordering_group_by = self.get_ordering()

tests/regressiontests/queries/tests.py

@@ -86,8 +86,18 @@ class EmptyQuerySetTests(TestCase):
     def test_emptyqueryset_values(self):
         "#14366 -- calling .values() on an EmptyQuerySet and then cloning that should not cause an error"
         self.assertEqual(list(Number.objects.none().values('num').order_by('num')), [])
-    
+
     def test_values_subquery(self):
         self.assertQuerysetEqual(
             Number.objects.filter(pk__in=Number.objects.none().values("pk")), []
         )
+
+
+class WeirdQuerySetSlicing(TestCase):
+    def setUp(self):
+        Number.objects.create(num=1)
+        Number.objects.create(num=2)
+
+    def test_empty_resultset_sql(self):
+        # ticket #12192
+        self.assertNumQueries(0, lambda: list(Number.objects.all()[1:1]))