Getting import error when importing db from app.py

app.py file

from flask import Flask
from flask_sqlalchemy import SQLAlchemy
from database import CreateQuestions

app = Flask(__name__)
app.config['SQLALCHEMY_DATABASE_URI'] = "postgres://jim:password@localhost:5433/exquizdb"
db = SQLAlchemy(app)


@app.route('/questions')
def post_question():
    q = 'hey'
    a = 'hi'
    CreateQuestions.Create_questions(q, a)


@app.route('/')
def hello_world():
    return 'Hello World!'


if __name__ == '__main__':
    app.run()

database.py

# database.py
from app import db


class Questions(db.Model):
    question_id = db.Column(db.Integer, primary_key=True)
    question = db.Column(db.Text)


class Answers(db.Model):
    answer_id = db.Column(db.Integer, primary_key=True)
    answer = db.Column(db.Text)
    question_id = db.Column(db.Integer, db.ForeignKey('questions.question_id'))


class CreateQuestions:
    def create_questions(self, q, a):
        ques = Questions(question=q)
        ans = Answers(answer=a)
        db.create_all()
        db.session.add(ques)
        db.session.add(ans)
        db.session.commit()

when I run the app, the crashes with 'ImportError: cannot import name 'db' from 'app''. I don't know what I am doing wrong. When I do them on the same file it works. when I takeout the database Model from the app.py file it doesnt work anymore. Thank you for your help