Python 在一个查询中使用func.max和func.count

我有两张桌子：

class Shops(db.Model):
    id = db.Column(db.Integer, primary_key = True)
    name = db.Column(db.String(255))
    order = db.relationship('Order', backref = 'purchased', lazy = 'dynamic')

class Order(db.Model):
    id = db.Column(db.Integer, primary_key = True)
    date = db.Column(db.DateTime)
    shop = db.Column(db.Integer, ForeignKey('shop.id'))

我想根据订单获得最畅销的店铺，如下所示：

query = db.session.query(Shops.name.label('TopShop'),Order,func.max(func.count(Order.shop)))

这会产生以下错误：

ProgrammingError: (ProgrammingError) (1111, u'Invalid use of group function') 

是否有正确方向的指针？

按订单数量排列的顶级商店：

subq = (session.query(Order.shop, func.count(Order.id).label("num_orders")).
        group_by(Order.shop)).subquery()
q = session.query(Shops).join(subq, Shops.id == subq.c.shop).order_by(subq.c.num_orders.desc())

# top 1
print q.first()
# top 5
print q[:5]