[Sqlalchemy-tickets] Issue #3657: positional result column logic failing (zzzeek/sqlalchemy)

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

New issue 3657: positional result column logic failing
https://bitbucket.org/zzzeek/sqlalchemy/issues/3657/positional-result-column-logic-failing

Mike Bayer:

Havent fully tracked this down yet, suspect the query wrapping in mssql for LIMIT/OFFSET is causing this to happen.

very heisenbuggy, set PYTHONHASHEED=random and run lots of times against mssql:


```
#!python

import sqlalchemy as sa
import sqlalchemy.orm as saorm
from sqlalchemy.ext.declarative import declarative_base

#engine = sa.create_engine('mssql+pymssql://badams:password@192.168.56.101:1443/testdb', echo=True)

engine = sa.create_engine('mssql+pymssql://scott:tiger@192.168.122.232:1213/test', echo=True)

session = saorm.sessionmaker(bind=engine)()

Base = declarative_base()

class Person(Base):
    __tablename__ = 'people'
    id = sa.Column(sa.Integer, primary_key=True)
    name = sa.Column(sa.String)

Base.metadata.create_all(engine)

session.query(Person).delete()

session.add(Person(name='foo'))
session.add(Person(name='bar'))

session.commit()

results = session.query(
    Person.name.label('person'),
).add_entity(
    Person
).order_by(
    Person.name
)

print results.count()
print results.limit(1).offset(1).all()


```

the stack is a lie; to really make this fail we have to raise here (and this is another issue for 1.1, why aren't we raising here? )

```
#!diff


--- a/lib/sqlalchemy/engine/result.py
+++ b/lib/sqlalchemy/engine/result.py
@@ -420,7 +427,8 @@ class ResultMetaData(object):
         if key in self._keymap:
             processor, obj, index = self._keymap[key]
         else:
-            ret = self._key_fallback(key, False)
+            # MARKMARK
+            ret = self._key_fallback(key) #, False)
             if ret is None:
                 return None
             processor, obj, index = ret

```


so ultimately the compiler._result_columns is wrong.  on a bad run its:


```
#!python

[

('person', 'person', (Column('name', String(), table=<people>), 'person', 'person'), String()), 
('people_id', 'people_id', (Column('id', Integer(), table=<people>, primary_key=True, nullable=False), 'people_id', 'people_id'), Integer()), ('people_name', 'people_name', (Column('name', String(), table=<people>), 'people_name', 'people_name'), String())

]

```

on a good run it's:

```
#!python


[

('person', 'person', (<sqlalchemy.sql.elements.Label object at 0x7f46cc3dcf10>, 'person', 'person'), String()), 
('people_id', 'people_id', (Column('id', Integer(), table=<people>, primary_key=True, nullable=False), 'people_id', 'people_id'), Integer()), ('people_name', 'people_name', (Column('name', String(), table=<people>), 'people_name', 'people_name'), String())
]

```

so our label is occasionally getting whacked from the result list, and its a dictionary ordering issue.   the LIMIT wrapping in mssql/base.py -> visit_select seems like it may be significant also.