In [1]: from app import db
In [2]: db.create_all()   # db.drop_all() 删除数据库
In [3]: from app import Student
In [4]: bob = Student('bob', 20, 'beijing')
In [5]: lily = Student('lily', 19, 'shanghai')
In [6]: db.session.add(bob)
In [7]: db.session.add(lily)
In [8]: db.session.commit()

mysql> select * from student;
+-----+-------+------+----------+
| sno | sname | sage | saddress |
+-----+-------+------+----------+
|   1 | bob   |   20 | beijing  |
|   2 | lily  |   19 | shanghai |
+-----+-------+------+----------+
2 rows in set (0.00 sec)

In [9]: Student.query.all()
Out[9]:
[Student({'sno': 1L,'sage': 20L, 'saddress': u'beijing', 'sname': u'bob'}),
 Student({'sno': 2L, 'sage': 19L, 'saddress': u'shanghai', 'sname': u'lily'})]

In [11]: Student.query.order_by(Student.sage.desc()).all()
Out[11]:
[Student({'sno': 1L, 'sage': 20L, 'saddress': u'beijing', 'sname': u'bob'}),
 Student({'sno': 2L, 'sage': 19L, 'saddress': u'shanghai', 'sname': u'lily'})]

In [12]: Student.query.order_by(Student.sage).all()
Out[12]:
[Student({'sno': 2L, 'sage': 19L, 'saddress': u'shanghai', 'sname': u'lily'}),
 Student({'sno': 1L, 'sage': 20L, 'saddress': u'beijing', 'sname': u'bob'})]

In [13]: Student.query.order_by(Student.sage).first()
Out[13]: Student({'sno': 2L, 'sage': 19L, 'saddress': u'shanghai', 'sname': u'lily'})

In [19]: Student.query.filter_by(sno=1).all()
Out[19]: [Student({'sno': 1L, 'sage': 20L, 'saddress': u'beijing', 'sname': u'bob'})]

In [14]: student = Student.query.filter_by(sno=1).first()
In [15]: student
Out[15]: Student({'sno': 1L, 'sage': 20L, 'saddress': u'beijing', 'sname': u'bob'})
In [16]: db.session.delete(student)
In [17]: db.session.commit()

@app.route('/user/<username>')
def show_user(username):
    user = User.query.filter_by(username=username).first_or_404()
    return render_template('show_user.html', user=user)