连接mysql数据库，创建用户模型

from flask import Flask
from flask_sqlalchemy import SQLAlchemy
import config

app = Flask(__name__)
app.config.from_object(config)
db=SQLAlchemy(app)

class User(db.Model):
    __tablename__='user'
    id=db.Column(db.Integer,primary_key=True,autoincrement=True)
    username = db.Column(db.String(20),nullable=False)
    password = db.Column(db.String(20),nullable=False)

db.create_all()

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


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