Use separate label generator for column_label naming convention

Fixed bug where a table that would have a column label overlap with a plain
column name, such as "foo.id AS foo_id" vs. "foo.foo_id", would prematurely
generate the ``._label`` attribute for a column before this overlap could
be detected due to the use of the ``index=True`` or ``unique=True`` flag on
the column in conjunction with the default naming convention of
``"column_0_label"``.  This would then lead to failures when ``._label``
were used later to generate a bound parameter name, in particular those
used by the ORM when generating the WHERE clause for an UPDATE statement.
The issue has been fixed by using an alternate ``._label`` accessor for DDL
generation that does not affect the state of the :class:`.Column`.   The
accessor also bypasses the key-deduplication step as it is not necessary
for DDL, the naming is now consistently ``"<tablename>_<columnname>"``
without any subsequent numeric symbols when used in DDL.

Fixes: #4911

Change-Id: Iabf5fd3250738d800d6e41a2a3a27a7ce2405e7d

1 files changed, 1 insertions, 1 deletions

diff --git a/lib/sqlalchemy/sql/naming.py b/lib/sqlalchemy/sql/naming.py
index 68a6190cf..3fca4e35b 100644
--- a/lib/sqlalchemy/sql/naming.py
+++ b/lib/sqlalchemy/sql/naming.py
@@ -67,7 +67,7 @@ class ConventionDict(object):
         return self._column_X(idx).name
 
     def _key_column_X_label(self, idx):
-        return self._column_X(idx)._label
+        return self._column_X(idx)._ddl_label
 
     def _key_referred_table_name(self):
         fk = self.const.elements[0]