OperationalError：无此类表：条目

我正在学习flask框架，并且正在按照flask教程学习。我逐行遵循了本教程的每个步骤。最后，我得到了错误“ sqlite3.OperationalError OperationalError：没有这样的表：entrys”。我在linux机器上，以前从未使用过sqlite。我不知道如何解决这个问题。而且flaskr.py的代码在下面

# all the imports
import os
import sqlite3
from flask import Flask, request, session, g, redirect, url_for, abort, render_template, flash



# create our little application :)
app = Flask(__name__)
app.config.from_object(__name__)
# Load default config and override config from an environment variable
app.config.update(dict(
DATABASE=os.path.join(app.root_path, 'flaskr.db'),
DEBUG=True,
SECRET_KEY='development key',
USERNAME='admin',
PASSWORD='default'
))
app.config.from_envvar('FLASKR_SETTINGS', silent=True)


def connect_db():
# """Connects to the specific database."""
    rv = sqlite3.connect(app.config['DATABASE'])
    rv.row_factory = sqlite3.Row
    return rv

def init_db():
    with app.app_context():
        db = get_db()
    with app.open_resource('schema.sql', mode='r') as f:
        db.cursor().executescript(f.read())
        db.commit()


def get_db():
#"""Opens a new database connection if there is none yet for the current application context."""
    if not hasattr(g, 'sqlite_db'):
        g.sqlite_db = connect_db()
        return g.sqlite_db


@app.teardown_appcontext
def close_db(error):
#"""Closes the database again at the end of the request."""
    if hasattr(g, 'sqlite_db'):
        g.sqlite_db.close()



@app.route('/')
def show_entries():
    db = get_db()
    cur = db.execute('select title, text from entries order by id desc')
    entries = cur.fetchall()
    return render_template('show_entries.html', entries=entries)



@app.route('/add', methods=['POST'])
def add_entry():
    if not session.get('logged_in'):
        abort(401)
        db = get_db()
        db.execute('insert into entries (title, text) values (?, ?)',
        [request.form['title'], request.form['text']])
        db.commit()
        flash('New entry was successfully posted')
    return redirect(url_for('show_entries'))



@app.route('/login', methods=['GET', 'POST'])
def login():
    error = None
    if request.method == 'POST':
        if request.form['username'] != app.config['USERNAME']:
            error = 'Invalid username'
        elif request.form['password'] != app.config['PASSWORD']:
            error = 'Invalid password'
        else:
            session['logged_in'] = True
            flash('You were logged in')
        return redirect(url_for('show_entries'))
    return render_template('login.html', error=error)


@app.route('/logout')
def logout():
    session.pop('logged_in', None)
    flash('You were logged out')
    return redirect(url_for('show_entries'))



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