Ticket #18330: django-ticket18330.diff

django/core/cache/backends/db.py

@@ -167 +167 @@
             num = cursor.fetchone()[0]
             if num > self._max_entries:
                 cull_num = num / self._cull_frequency
-                if connections[db].vendor == 'oracle':
-                    # Oracle doesn't support LIMIT + OFFSET
-                    cursor.execute("""SELECT cache_key FROM
-(SELECT ROW_NUMBER() OVER (ORDER BY cache_key) AS counter, cache_key FROM %s)
-WHERE counter > %%s AND COUNTER <= %%s""" % table, [cull_num, cull_num + 1])
-                else:
-                    # This isn't standard SQL, it's likely to break
-                    # with some non officially supported databases
-                    cursor.execute("SELECT cache_key FROM %s "
-                                   "ORDER BY cache_key "
-                                   "LIMIT 1 OFFSET %%s" % table, [cull_num])
+
+                sql, params = connections[db].ops.raw_limit_offset_select(
+                    fields='cache_key',
+                    table=table,
+                    order_by='cache_key',
+                    limit=1,
+                    offset=cull_num,
+                )
+                cursor.execute(sql, params)
+
                 cursor.execute("DELETE FROM %s "
                                "WHERE cache_key < %%s" % table,
                                [cursor.fetchone()[0]])

django/db/backends/__init__.py

@@ -874 +874 @@
         conn = ' %s ' % connector
         return conn.join(sub_expressions)
 
+    def raw_limit_offset_select(self, fields, table, limit, offset=None, where=None, order_by=None):
+        """
+        Returns a two element tuple with the raw SQL string to do a simple 
+        select with limit + offset and a list of parameters to provide to the 
+        cursor with the SQL.
+
+        It is the caller's responsibilty to properly quote any entities in
+        `fields`, `table`, and `order_by`.
+        """
+        params = []
+        sql = "SELECT %s FROM %s" % (fields, table)
+        if where:
+            sql += " WHERE %s" % where
+        if order_by:
+              sql += " ORDER BY %s " % order_by
+        if limit:
+            sql += " LIMIT %s"
+            params.append(limit)
+            if offset:
+                sql += " OFFSET %s"
+                params.append(offset)
+        return sql, params
+
 class BaseDatabaseIntrospection(object):
     """
     This class encapsulates all backend-specific introspection utilities

django/db/backends/oracle/base.py

@@ -389 +389 @@
         items_sql = "SELECT %s FROM DUAL" % ", ".join(["%s"] * len(fields))
         return " UNION ALL ".join([items_sql] * num_values)
 
+    def raw_limit_offset_select(self, fields, table, limit, offset=None, where=None, order_by=None):
+        sql = "SELECT %s FROM " \
+              "(SELECT ROW_NUMBER() OVER (ORDER BY cache_key) AS counter, %s" \
+              " FROM %s)" % (fields, fields, table)
+        where_parts, params = [], []
+        if where:
+            where_parts.append('(%s)' % where)
+        if offset is not None:
+            where_parts.append('counter > %s')
+            params.append(offset)
+        if limit is not None:
+            where_parts.append('counter <= %s')
+            params.append((offset + limit) if offset else limit)
+        if where_parts:
+            sql += ' WHERE %s' % ' AND '.join(where_parts)
+        return sql, params
 
 class _UninitializedOperatorsDescriptor(object):
 

tests/regressiontests/aggregation_regress/tests.py

@@ -6 +6 @@
 from operator import attrgetter
 
 from django.core.exceptions import FieldError
+from django.db import connection
 from django.db.models import Count, Max, Avg, Sum, StdDev, Variance, F, Q
 from django.test import TestCase, Approximate, skipUnlessDBFeature
 
@@ -66 +67 @@
         Regression test for #11916: Extra params + aggregation creates
         incorrect SQL.
         """
-        #oracle doesn't support subqueries in group by clause
-        shortest_book_sql = """
-        SELECT name
-        FROM aggregation_regress_book b
-        WHERE b.publisher_id = aggregation_regress_publisher.id
-        ORDER BY b.pages
-        LIMIT 1
-        """
+        qn = connection.ops.quote_name
+        sql, params = connection.ops.raw_limit_offset_select(
+            fields=qn('name'),
+            table=qn('aggregation_regress_book'),
+            where='%s = %s.%s' % (qn('publisher_id'), qn('aggregation_regress_publisher'), qn('id')),
+            order_by=qn('pages'),
+            limit=1,
+        )
+        shortest_book_sql = sql % params[0]
         # tests that this query does not raise a DatabaseError due to the full
         # subselect being (erroneously) added to the GROUP BY parameters
         qs = Publisher.objects.extra(select={