SQLAlchemy核心生成PostgreSQL子串表达式？

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

# 创建数据库连接
engine = create_engine('postgresql://username:password@localhost/db_name')

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

# 创建基类
Base = declarative_base()

# 创建模型类
class MyTable(Base):
    __tablename__ = 'my_table'
    id = Column(Integer, primary_key=True)
    text = Column(String)

# 生成子串表达式查询
subquery = session.query(func.substr(MyTable.text, 2, 5))

# 执行查询
results = subquery.all()

# 输出结果
for result in results:
    print(result)