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, 20 insertions, 0 deletions

diff --git a/test/sql/test_update.py b/test/sql/test_update.py
index 9309ca45a..e625b7d9c 100644
--- a/test/sql/test_update.py
+++ b/test/sql/test_update.py
@@ -292,6 +292,26 @@ class UpdateTest(_UpdateFromTestBase, fixtures.TablesTest, AssertsCompiledSQL):
             "UPDATE foo SET id=:id, foo_id=:foo_id WHERE foo.id = :foo_id_1",
         )
 
+    def test_labels_no_collision_index(self):
+        """test for [ticket:4911] """
+
+        t = Table(
+            "foo",
+            MetaData(),
+            Column("id", Integer, index=True),
+            Column("foo_id", Integer),
+        )
+
+        self.assert_compile(
+            t.update().where(t.c.id == 5),
+            "UPDATE foo SET id=:id, foo_id=:foo_id WHERE foo.id = :id_1",
+        )
+
+        self.assert_compile(
+            t.update().where(t.c.id == bindparam(key=t.c.id._label)),
+            "UPDATE foo SET id=:id, foo_id=:foo_id WHERE foo.id = :foo_id_1",
+        )
+
     def test_inline_defaults(self):
         m = MetaData()
         foo = Table("foo", m, Column("id", Integer))