1 files changed, 50 insertions, 3 deletions

diff --git a/lib/sqlalchemy/sql.py b/lib/sqlalchemy/sql.py
index 273af5415..9c8d5db08 100644
--- a/lib/sqlalchemy/sql.py
+++ b/lib/sqlalchemy/sql.py
@@ -1549,8 +1549,55 @@ class Join(FromClause):
     def _group_parenthesized(self):
         return True
 
-    def select(self, whereclauses = None, **params):
-        return select([self.left, self.right], whereclauses, from_obj=[self], **params)
+    def _get_folded_equivalents(self, equivs=None):
+        if equivs is None:
+            equivs = util.Set()
+        class LocateEquivs(ClauseVisitor):
+            def visit_binary(self, binary):
+                if binary.operator == '=' and binary.left.name == binary.right.name:
+                    equivs.add(binary.right)
+                    equivs.add(binary.left)
+        self.onclause.accept_visitor(LocateEquivs())
+        collist = []
+        if isinstance(self.left, Join):
+            left = self.left._get_folded_equivalents(equivs)
+        else:
+            left = list(self.left.columns)
+        if isinstance(self.right, Join):
+            right = self.right._get_folded_equivalents(equivs)
+        else:
+            right = list(self.right.columns)
+        used = util.Set()
+        for c in left + right:
+            if c in equivs:
+                if c.name not in used:
+                    collist.append(c)
+                    used.add(c.name)
+            else: 
+                collist.append(c)
+        return collist
+        
+    def select(self, whereclause = None, fold_equivalents=False, **kwargs):
+        """Create a ``Select`` from this ``Join``.
+        
+        whereclause
+          the WHERE criterion that will be sent to the ``select()`` function
+          
+        fold_equivalents
+          based on the join criterion of this ``Join``, do not include equivalent
+          columns in the column list of the resulting select.  this will recursively
+          apply to any joins directly nested by this one as well.
+          
+        **kwargs
+          all other kwargs are sent to the underlying ``select()`` function
+          
+        """
+        if fold_equivalents:
+            collist = self._get_folded_equivalents()
+        else:
+            collist = [self.left, self.right]
+            
+        return select(collist, whereclause, from_obj=[self], **kwargs)
 
     def accept_visitor(self, visitor):
         self.left.accept_visitor(visitor)
@@ -1912,7 +1959,7 @@ class Select(_SelectBaseMixin, FromClause):
         self.offset = offset
         self.for_update = for_update
         self.is_compound = False
-
+        
         # indicates that this select statement should not expand its columns
         # into the column clause of an enclosing select, and should instead
         # act like a single scalar column