增加：
db.session.add(user)
db.session.commit()
查询：
User.query.filter(User.username == 'mis1114').first()
修改：
user.password = '111111'
db.session.commit()
删除：
db.session.delete(user)
db.session.commit()
1 user = User(username = 'misjiaojiao',password = 'misjiaojiao')
2 db.session.add(user)
3 db.session.commit()
4 #增
5
6 user = User.query.filter(User.username == 'misjiaojiao').first()
7 db.session.delete(user)
8 db.session.commit()
9 #删
10
11 user = User.query.filter(User.username == 'misjiaojiao').first()
12 user.password='1234657'
13 db.session.commit()
14 #改
15
16 user = User.query.filter(User.username == 'misjiaojiao').first()
17 print(user.username,user,password)
18 #查
