如何检查SqlAlchemy中的查询是否返回空结果？

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

Base = declarative_base()

class User(Base):
    __tablename__ = 'users'
    id = Column(Integer, primary_key=True)
    name = Column(String)

engine = create_engine('sqlite:///:memory:')
Base.metadata.create_all(engine)
Session = sessionmaker(bind=engine)
session = Session()

# 假设我们有一个查询
query = session.query(User).filter(User.name == 'John')

# 检查查询结果是否为空
if query.count() == 0:
    print("查询结果为空")
else:
    print("查询结果不为空")

result = query.first()
if result is None:
    print("查询结果为空")
else:
    print("查询结果不为空")

results = query.all()
if len(results) == 0:
    print("查询结果为空")
else:
    print("查询结果不为空")

if not query.exists():
    print("查询结果为空")
else:
    print("查询结果不为空")