Index: django/db/models/sql/query.py
===================================================================
--- django/db/models/sql/query.py	(revision 8448)
+++ django/db/models/sql/query.py	(working copy)
@@ -541,13 +541,20 @@
                 result.append('%s%s%s' % (connector, qn(name), alias_str))
             first = False
         for t in self.extra_tables:
+            if isinstance(t, tuple):
+                t, subselect = t
+            else:
+                subselect = None
             alias, unused = self.table_alias(t)
             # Only add the alias if it's not already present (the table_alias()
             # calls increments the refcount, so an alias refcount of one means
             # this is the only reference.
             if alias not in self.alias_map or self.alias_refcount[alias] == 1:
                 connector = not first and ', ' or ''
-                result.append('%s%s' % (connector, qn(alias)))
+                if subselect is None:
+                    result.append('%s%s' % (connector, qn(alias)))
+                else:
+                    result.append('%s%s as %s' % (connector, subselect, qn(alias)))
                 first = False
         return result, []
 
@@ -1560,7 +1567,11 @@
         if params:
             self.extra_params += tuple(params)
         if tables:
-            self.extra_tables += tuple(tables)
+            # allow tables to be dictionaries mapping names to subselects
+            if hasattr(tables, 'items'):
+                self.extra_tables += tuple(tables.items())
+            else:
+                self.extra_tables += tuple(tables)
         if order_by:
             self.extra_order_by = order_by