[Sqlalchemy-tickets] Issue #4304: why does query.statement add no_replacement_traverse (zzzeek/sqlalchemy)

[Michael B. <iss...@bi...>]

New issue 4304: why does query.statement add no_replacement_traverse
https://bitbucket.org/zzzeek/sqlalchemy/issues/4304/why-does-querystatement-add

Michael Bayer:

e.g.


```
#!diff

diff --git a/lib/sqlalchemy/orm/query.py b/lib/sqlalchemy/orm/query.py
index 272fed3e23..c623f10a95 100644
--- a/lib/sqlalchemy/orm/query.py
+++ b/lib/sqlalchemy/orm/query.py
@@ -514,7 +514,7 @@ class Query(object):
 
         # TODO: there's no tests covering effects of
         # the annotation not being there
-        return stmt._annotate({'no_replacement_traverse': True})
+        return stmt
 
     def subquery(self, name=None, with_labels=False, reduce_columns=False):
         """return the full SELECT statement represented by

```

here is a confusing effect of it being there:


```
#!python

from sqlalchemy import *
from sqlalchemy.orm import *
from sqlalchemy.ext.declarative import declarative_base

Base = declarative_base()


class MyTable(Base):
    __tablename__ = 'my_table'
    score = Column(Integer, primary_key=True)

my_alias = aliased(MyTable, name="my_alias")

s = Session()

query_2 = s.query(MyTable).union(s.query(MyTable))

query_2 = query_2.filter(MyTable.score > 5)

stmt1 = exists().where(my_alias.score > MyTable.score)
stmt2 = s.query(my_alias).filter(my_alias.score > MyTable.score).exists()

print(query_2.add_column(stmt1))

print(query_2.add_column(stmt2))

```


```
#!sql

# correct:
SELECT anon_1.my_table_score AS anon_1_my_table_score, EXISTS (SELECT * 
FROM my_table AS my_alias 
WHERE my_alias.score > anon_1.my_table_score) AS anon_2 
FROM (SELECT my_table.score AS my_table_score 
FROM my_table UNION SELECT my_table.score AS my_table_score 
FROM my_table) AS anon_1 
WHERE anon_1.my_table_score > :score_1

# incorrect:
SELECT anon_1.my_table_score AS anon_1_my_table_score, EXISTS (SELECT 1 
FROM my_table AS my_alias, my_table 
WHERE my_alias.score > my_table.score) AS anon_2 
FROM (SELECT my_table.score AS my_table_score 
FROM my_table UNION SELECT my_table.score AS my_table_score 
FROM my_table) AS anon_1 
WHERE anon_1.my_table_score > :score_1

```