- join() will now simulate a NATURAL JOIN by default. Meaning,

if the left side is a join, it will attempt to join the right
side to the rightmost side of the left first, and not raise
any exceptions about ambiguous join conditions if successful
even if there are further join targets across the rest of
the left.  [ticket:1714]

1 files changed, 6 insertions, 2 deletions

diff --git a/lib/sqlalchemy/sql/expression.py b/lib/sqlalchemy/sql/expression.py
index 9bc127291..1e02ba96a 100644
--- a/lib/sqlalchemy/sql/expression.py
+++ b/lib/sqlalchemy/sql/expression.py
@@ -2853,11 +2853,15 @@ class Join(FromClause):
     def get_children(self, **kwargs):
         return self.left, self.right, self.onclause
 
-    def _match_primaries(self, primary, secondary):
+    def _match_primaries(self, left, right):
         global sql_util
         if not sql_util:
             from sqlalchemy.sql import util as sql_util
-        return sql_util.join_condition(primary, secondary)
+        if isinstance(left, Join):
+            left_right = left.right
+        else:
+            left_right = None
+        return sql_util.join_condition(left, right, a_subset=left_right)
 
     def select(self, whereclause=None, fold_equivalents=False, **kwargs):
         """Create a :class:`Select` from this :class:`Join`.