- A refinement to the logic which adds columns to the resulting SQL when

:meth:`.Query.distinct` is combined with :meth:`.Query.order_by` such
that columns which are already present will not be added
a second time, even if they are labeled with a different name.
Regardless of this change, the extra columns added to the SQL have
never been returned in the final result, so this change only impacts
the string form of the statement as well as its behavior when used in
a Core execution context.   Additionally, columns are no longer added
when the DISTINCT ON format is used, provided the query is not
wrapped inside a subquery due to joined eager loading.
fixes #3641

1 files changed, 11 insertions, 15 deletions

diff --git a/lib/sqlalchemy/orm/query.py b/lib/sqlalchemy/orm/query.py
index 08600c357..8a25f570a 100644
--- a/lib/sqlalchemy/orm/query.py
+++ b/lib/sqlalchemy/orm/query.py
@@ -3254,12 +3254,11 @@ class Query(object):
         # then append eager joins onto that
 
         if context.order_by:
-            order_by_col_expr = list(
-                chain(*[
-                    sql_util.unwrap_order_by(o)
-                    for o in context.order_by
-                ])
-            )
+            order_by_col_expr = \
+                sql_util.expand_column_list_from_order_by(
+                    context.primary_columns,
+                    context.order_by
+                )
         else:
             context.order_by = None
             order_by_col_expr = []
@@ -3319,15 +3318,12 @@ class Query(object):
         if not context.order_by:
             context.order_by = None
 
-        if self._distinct and context.order_by:
-            order_by_col_expr = list(
-                chain(*[
-                    sql_util.unwrap_order_by(o)
-                    for o in context.order_by
-                ])
-            )
-            context.primary_columns += order_by_col_expr
-
+        if self._distinct is True and context.order_by:
+            context.primary_columns += \
+                sql_util.expand_column_list_from_order_by(
+                    context.primary_columns,
+                    context.order_by
+                )
         context.froms += tuple(context.eager_joins.values())
 
         statement = sql.select(