SqlAlchemey空值关系中的最后一个顺序

from sqlalchemy import create_engine, Column, Integer, String, DateTime, ForeignKey
from sqlalchemy.orm import relationship, Session
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.sql import func

Base = declarative_base()

class User(Base):
    __tablename__ = 'users'
    id = Column(Integer, primary_key=True)
    name = Column(String)
    orders = relationship("Order", back_populates="user")

class Order(Base):
    __tablename__ = 'orders'
    id = Column(Integer, primary_key=True)
    user_id = Column(Integer, ForeignKey('users.id'))
    created_at = Column(DateTime, nullable=True)
    user = relationship("User", back_populates="orders")

engine = create_engine('sqlite:///:memory:')
Base.metadata.create_all(engine)

session = Session(engine)

# 添加示例数据
# ...

# 查询并按订单创建日期排序，空值放在最后
users_sorted_by_order_date = session.query(User).join(Order).order_by(func.coalesce(Order.created_at, func.max(Order.created_at))).all()