Need a query in Sqlalchemy with GROUP BY CASE - sql-server

Question

All i need is a simple query with GROUP BY CASE like
SELECT
COUNT([Personnel].[PERSONNEL_ID]) AS value,
CASE
WHEN ([Personnel].[T_FIRSTNAME] = 'John') THEN 'John'
ELSE 'somethingelse'
END AS somelabel
FROM [Personnel]
GROUP BY
CASE
WHEN ([Personnel].[T_FIRSTNAME] = 'John') THEN 'John'
ELSE 'somethingelse'
END
in Sqlalchemy my query looks like this:
case_groups = case(
[(HrPersonnel.T_FIRSTNAME=='John', 'John')],
else_='somethingelse'
)
volunteers = session_mssql.query(
func.count(HrPersonnel.S_HR_PERSONNEL_ID).label('value'),
case_groups.label('somelabel'))\
.group_by(case_groups)\
.all()
mssql server executes the query without any problem (engine.connect().execute(text_query))
but Sqlalchemy ORM query gives me an error.
File
"c:\projects\sa_test\eggs\sqlalchemy-0.9.2-py2.7.egg\sqlalchemy\engine\default.py",
line 425, in do_execute cursor.execute(statement, parameters)
sqlalchemy.exc.ProgrammingError: (ProgrammingError) ('42000', "[42000]
[Microsoft][ODBC SQL Server Driver][SQL Server] Column
'Personnel.T_FIRSTNAME' is invalid in the select list because it is
not contained in either an aggregate function or the GROUP BY clause.
(8120) (SQLExecDirectW); [42000] [Microsoft][ODBC SQL Server
Driver][SQL Server]Statement(s) could not be prepared. (8180)")
u'SELECT count([Personnel].[PERSONNEL_ID]) AS value, CASE WHEN
([Personnel].[T_FIRSTNAME] = ?) THEN ? ELSE ? END AS somelabel \nFROM
[Personnel] GROUP BY CASE WHEN ([Personnel].[T_FIRSTNAME] = ?) THEN ?
ELSE ? END' ('John', 'John', 'somethingelse', 'John', 'John',
'somethingelse')
Why 'Personnel.T_FIRSTNAME' is invalid in the select list?
any suggestions are welcome.
Thanks,

Answer 1

I don't have an answer per se (although future readers may want to check this thread on the SQLAlchemy Google Group), but I've had a similar issue recently and found a workaround.
Instead of executing the query directly, convert it into a string and execute that. For example:
session.execute(
str(query.selectable.compile(compile_kwargs={'literal_binds': True}))
).fetchall()