SQLALCHEMY:子查询select出现问题，如何使用outerjoin进行精确子查询？

from sqlalchemy import create_engine, Column, Integer, String, ForeignKey
from sqlalchemy.orm import sessionmaker, relationship
from sqlalchemy.ext.declarative import declarative_base

# 创建数据库连接
engine = create_engine('数据库连接字符串')

# 创建会话
Session = sessionmaker(bind=engine)
session = Session()

# 定义模型
Base = declarative_base()

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

class Post(Base):
    __tablename__ = 'posts'
    id = Column(Integer, primary_key=True)
    title = Column(String)
    user_id = Column(Integer, ForeignKey('users.id'))
    user = relationship('User', back_populates='posts')

# 进行精确子查询
subquery = session.query(Post.user_id).filter(Post.title == 'example').subquery()
query = session.query(User).outerjoin(subquery, User.id == subquery.c.user_id).filter(subquery.c.user_id == None)

# 执行查询
results = query.all()

# 输出结果
for user in results:
    print(user.name)