* 겪고 있는 문제 상황을 최대한 자세하게 작성해주세요.

* 문제 해결을 위해 어떤 시도를 해보았는지 구체적으로 함께 알려주세요.

4-3 강의 내용 중, 터미널에서 flask shell. 을 입력하면 강사님처럼 되지 않고 에러가 납니다.

작성한 코드 및 에러 메세지

$ flask shell
Traceback (most recent call last):
  File "<frozen runpy>", line 198, in _run_module_as_main
  File "<frozen runpy>", line 88, in _run_code
  File "C:\Users\Seung-hyun Kim\Desktop\sparta\DB\.venv\Scripts\flask.exe\__main__.py", line 6, in <module>
    sys.exit(main())
             ~~~~^^
  File "c:\Users\Seung-hyun Kim\Desktop\sparta\DB\.venv\Lib\site-packages\flask\cli.py", line 1131, in main
    cli.main()
    ~~~~~~~~^^
  File "c:\Users\Seung-hyun Kim\Desktop\sparta\DB\.venv\Lib\site-packages\click\core.py", line 1363, in main
    rv = self.invoke(ctx)
  File "c:\Users\Seung-hyun Kim\Desktop\sparta\DB\.venv\Lib\site-packages\click\core.py", line 1830, in invoke
    return _process_result(sub_ctx.command.invoke(sub_ctx))
                           ~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^
  File "c:\Users\Seung-hyun Kim\Desktop\sparta\DB\.venv\Lib\site-packages\click\core.py", line 1226, in invoke
    return ctx.invoke(self.callback, **ctx.params)
           ~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "c:\Users\Seung-hyun Kim\Desktop\sparta\DB\.venv\Lib\site-packages\click\core.py", line 794, in invoke
    return callback(*args, **kwargs)
  File "c:\Users\Seung-hyun Kim\Desktop\sparta\DB\.venv\Lib\site-packages\click\decorators.py", line 34, in new_func
    return f(get_current_context(), *args, **kwargs)
  File "c:\Users\Seung-hyun Kim\Desktop\sparta\DB\.venv\Lib\site-packages\flask\cli.py", line 397, in decorator
    app = ctx.ensure_object(ScriptInfo).load_app()
  File "c:\Users\Seung-hyun Kim\Desktop\sparta\DB\.venv\Lib\site-packages\flask\cli.py", line 353, in load_app
    app = locate_app(import_name, None, raise_if_not_found=False)
  File "c:\Users\Seung-hyun Kim\Desktop\sparta\DB\.venv\Lib\site-packages\flask\cli.py", line 245, in locate_app
    __import__(module_name)
    ~~~~~~~~~~^^^^^^^^^^^^^
  File "C:\Users\Seung-hyun Kim\Desktop\sparta\DB\app.py", line 10, in <module>
    class Song(db.Model):
               ^^
NameError: name 'db' is not defined
(.venv) 
Seung-hyun Kim@DESKTOP-9O9F9C5 MINGW64 ~/Desktop/sparta/DB
$