关于使用python对数据库排序的问题

Question

import requests
from multiprocessing import Pool
from bs4 import BeautifulSoup
import pymysql
import time


def prepare_url():
    base_url = "https://movie.douban.com/top250?start="
    full_urls = []
    for i in range(0, 10):
        # 准备全路径
        full_url = base_url + str(i * 25)
        full_urls.append(full_url)
    return full_urls


def get_html(url):
    headers = {
        "User-Agent": "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/85.0.4183.121 Safari/537.36 Edg/85.0.564.68"}
    try:
        html = requests.get(url=url, headers=headers).content.decode('utf-8')
    except:
        print("爬取失败")
    return html



def parse_html(html):
    soup = BeautifulSoup(html, 'html.parser')
    div_list = soup.find_all('div', {'class': 'info'})
    message_list = []
    for div in div_list:
        title = div.find('a').find('span').text
        score = div.find('div', {'class': 'star'}).find('span', {'class': 'rating_num'}).text
        movie_url = div.find('a')['href']

        dict = {'movie': title, 'rating_num': score, 'url': movie_url}
        message_list.append(dict)

    return message_list

def prepareDatabase():
    db = pymysql.connect("localhost", 'root', '123456', 'test')
    cursor = db.cursor()
    sql = """
            CREATE TABLE IF NOT EXISTS data (
                url VARCHAR(255) NOT NULL ,
                movie_name VARCHAR(255) NOT NULL,
                rating_num FLOAT NOT NULL,
                PRIMARY KEY(url)
            )
    """
    cursor.execute(sql)
    sql_utf = "ALTER TABLE data CONVERT TO CHARACTER SET utf8 COLLATE utf8_general_ci;"
    cursor.execute(sql_utf)
    db.close()


def save_data(url,movie,rating_num):
    db = pymysql.connect("localhost", 'root', '123456', 'test')
    cursor = db.cursor()
    sql = 'INSERT INTO data(url,movie_name,rating_num) VALUES ("{}","{}",{})'
    try:
        cursor.execute(sql.format(url,movie,rating_num))
        db.commit()
    except:
        db.rollback()
    db.close()

# 试图给数据库中的数据进行降序排序
def sort():
    db = pymysql.connect("localhost", 'root', '123456', 'test')
    cursor = db.cursor()
    sql = "SELECT * FROM data order by rating_num desc"
    try:
        cursor.execute(sql)
        db.commit()
    except:
        db.rollback()
    db.close()

def get_data(url):
    html = get_html(url)
    datas = parse_html(html)
    prepareDatabase()
    for i in range(0,len(datas)):
        save_data(datas[i]['url'],datas[i]['movie'],datas[i]['rating_num'])



if __name__ == '__main__':
    start_time = time.time()
    full_urls = prepare_url()
    pool = Pool(19)
    pool.map(get_data,full_urls)
    sort()
    end_time = time.time()
    print("Run time = " + str(end_time - start_time) + " Second.")
    # data_save()

程序没有报错，但是没办法对爬取之后保存到数据库中的数据进行排序，是python不能对数据库进行排序操作吗，我看的书上也没有，人要傻了

Answer 1

SELECT * FROM data order by rating_num desc

这句代码的意思是查询的时候排序，并不改变数据库中的数据本身