1 files changed, 20 insertions, 3 deletions
diff --git a/lib/sqlalchemy/sql/util.py b/lib/sqlalchemy/sql/util.py
index 8f502fc86..f5aa9f228 100644
--- a/lib/sqlalchemy/sql/util.py
+++ b/lib/sqlalchemy/sql/util.py
@@ -154,6 +154,7 @@ def unwrap_order_by(clause):
     without DESC/ASC/NULLS FIRST/NULLS LAST"""
 
     cols = util.column_set()
+    result = []
     stack = deque([clause])
     while stack:
         t = stack.popleft()
@@ -166,11 +167,13 @@ def unwrap_order_by(clause):
                 t = t.element
             if isinstance(t, (_textual_label_reference)):
                 continue
-            cols.add(t)
+            if t not in cols:
+                cols.add(t)
+                result.append(t)
         else:
             for c in t.get_children():
                 stack.append(c)
-    return cols
+    return result
 
 
 def clause_is_present(clause, search):
@@ -200,6 +203,21 @@ def surface_selectables(clause):
             stack.append(elem.element)
 
 
+def surface_column_elements(clause):
+    """traverse and yield only outer-exposed column elements, such as would
+    be addressable in the WHERE clause of a SELECT if this element were
+    in the columns clause."""
+
+    stack = deque([clause])
+    while stack:
+        elem = stack.popleft()
+        yield elem
+        for sub in elem.get_children():
+            if isinstance(sub, FromGrouping):
+                continue
+            stack.append(sub)
+
+
 def selectables_overlap(left, right):
     """Return True if left/right have some overlapping selectable"""
 
@@ -433,7 +451,6 @@ def criterion_as_pairs(expression, consider_as_foreign_keys=None,
     return pairs
 
 
-
 class ClauseAdapter(visitors.ReplacingCloningVisitor):
     """Clones and modifies clauses based on column correspondence.