SQLAlchemy的count很慢

http://docs.sqlalchemy.org/en/rel_0_8/orm/tutorial.html#counting

uall = User.query.count()
很慢 (subquery的關係?)

session.query(func.count(User.id)).scalar()
快多了

232,053的資料, 用time.time() 算

count(): 4.53022193909 sec
func.count: 0.17828607559 sec