Coursera课程《Using Databases with Python》 密歇根大学

Week3 Data Models and Relational SQL

15.4 Designing a Data Model

主要介绍了数据模型的重要性,以及数据模型构建的一些思考过程。

15.5 Representing a Data Model in Tables

概念模型

主键(Primary key),指的是一个列或多列的组合,其值能唯一地标识表中的每一行,通过它可强制表的实体完整性。主键主要是用于其他表的外键关联,以及本记录的修改与删除。

外键(Foreign key),作用是保持数据一致性,完整性,主要目的是控制存储在外键表中的数据。 使两张表形成关联,外键只能引用外表中的列的值。

如果我们要构建上面概念模型所表示的数据库,那么我们用到的一些SQL语句有:

CREATE TABLE Genre(
id INTEGER NOT NULL PRIMARY KEY AUTOINCREMENT UNIQUE,
name TEXT
)
CREATE TABLE Album(
id INTEGER NOT NULL PRIMARY KEY AUTOINCREMENT UNIQUE,
artist_id INTEGER
title TEXT
)
CREATE TABLE Track(
id INTEGER NOT NULL PRIMARY KEY
AUTOINCREMENT UNIQUE,
title TEXT,
album_id INTEGER,
genre_id INTEGER,
len INTEGER,
rating INTEGER,
count INTEGER
)

15.6 Inserting Relational Data

插入数据

insert into Artist(name) values ('Led Zepplin')
insert into Artist(name) values ('AC/DC')

像上面这样就往Artist表中加入了两行数据。

而对于Album表来说,它连接了Artist表,有两列数据要插入,那么这样。

insert into Album(title,artist_id) values ('Who Made Who',2)
insert into Album(title,artist_id) values ('IV',1)

所以这样之后,我们就建立起了数据之间的关系。

15.7 Reconstructing Data with JOIN

JOIN操作像是在几个表之间的SELECT操作。

而我们告诉JOIN怎么使用这些key则需要用到ON语句。有点像WHERE语句。

select Album.title, Artist.name from Album join Artist on Album.artist_id = Artist.id

如果把事情变复杂一些……

Work Example: Tracks.py

import xml.etree.ElementTree as ET
import sqlite3 conn = sqlite3.connect('trackdb.sqlite')
cur = conn.cursor() # Make some fresh tables using executescript()
cur.executescript('''
DROP TABLE IF EXISTS Artist;
DROP TABLE IF EXISTS Album;
DROP TABLE IF EXISTS Track; CREATE TABLE Artist (
id INTEGER NOT NULL PRIMARY KEY AUTOINCREMENT UNIQUE,
name TEXT UNIQUE
); CREATE TABLE Album (
id INTEGER NOT NULL PRIMARY KEY AUTOINCREMENT UNIQUE,
artist_id INTEGER,
title TEXT UNIQUE
); CREATE TABLE Track (
id INTEGER NOT NULL PRIMARY KEY
AUTOINCREMENT UNIQUE,
title TEXT UNIQUE,
album_id INTEGER,
len INTEGER, rating INTEGER, count INTEGER
);
''') fname = input('Enter file name: ')
if ( len(fname) < 1 ) : fname = 'Library.xml' # <key>Track ID</key><integer>369</integer>
# <key>Name</key><string>Another One Bites The Dust</string>
# <key>Artist</key><string>Queen</string>
def lookup(d, key):
found = False
for child in d:
if found : return child.text
if child.tag == 'key' and child.text == key :
found = True
return None stuff = ET.parse(fname)
all = stuff.findall('dict/dict/dict')
print('Dict count:', len(all))
for entry in all:
if ( lookup(entry, 'Track ID') is None ) : continue name = lookup(entry, 'Name')
artist = lookup(entry, 'Artist')
album = lookup(entry, 'Album')
count = lookup(entry, 'Play Count')
rating = lookup(entry, 'Rating')
length = lookup(entry, 'Total Time') if name is None or artist is None or album is None :
continue print(name, artist, album, count, rating, length) cur.execute('''INSERT OR IGNORE INTO Artist (name)
VALUES ( ? )''', ( artist, ) )
cur.execute('SELECT id FROM Artist WHERE name = ? ', (artist, ))
artist_id = cur.fetchone()[0] cur.execute('''INSERT OR IGNORE INTO Album (title, artist_id)
VALUES ( ?, ? )''', ( album, artist_id ) )
cur.execute('SELECT id FROM Album WHERE title = ? ', (album, ))
album_id = cur.fetchone()[0] cur.execute('''INSERT OR REPLACE INTO Track
(title, album_id, len, rating, count)
VALUES ( ?, ?, ?, ?, ? )''',
( name, album_id, length, rating, count ) ) conn.commit()

使用python脚本建立数据库的过程,注意其中的关键字IGNORE,它的作用是如果当期数据存在,那就不插入,否则插入。在这个地方十分有用,因为索引不能随意变化。

作业代码

import xml.etree.ElementTree as ET
import sqlite3 conn = sqlite3.connect('trackdb.sqlite')
cur = conn.cursor() # Make some fresh tables using executescript()
cur.executescript('''
DROP TABLE IF EXISTS Artist;
DROP TABLE IF EXISTS Album;
DROP TABLE IF EXISTS Track;
DROP TABLE IF EXISTS Genre; CREATE TABLE Artist (
id INTEGER NOT NULL PRIMARY KEY AUTOINCREMENT UNIQUE,
name TEXT UNIQUE
); CREATE TABLE Genre (
id INTEGER NOT NULL PRIMARY KEY AUTOINCREMENT UNIQUE,
name TEXT UNIQUE
); CREATE TABLE Album (
id INTEGER NOT NULL PRIMARY KEY AUTOINCREMENT UNIQUE,
artist_id INTEGER,
title TEXT UNIQUE
); CREATE TABLE Track (
id INTEGER NOT NULL PRIMARY KEY
AUTOINCREMENT UNIQUE,
title TEXT UNIQUE,
album_id INTEGER,
genre_id INTEGER,
len INTEGER, rating INTEGER, count INTEGER
);
''') fname = input('Enter file name: ')
if ( len(fname) < 1 ) : fname = 'Library.xml' # <key>Track ID</key><integer>369</integer>
# <key>Name</key><string>Another One Bites The Dust</string>
# <key>Artist</key><string>Queen</string>
def lookup(d, key):
found = False
for child in d:
if found : return child.text
if child.tag == 'key' and child.text == key :
found = True
return None stuff = ET.parse(fname)
all = stuff.findall('dict/dict/dict')
print('Dict count:', len(all))
for entry in all:
if ( lookup(entry, 'Track ID') is None ) : continue name = lookup(entry, 'Name')
artist = lookup(entry, 'Artist')
album = lookup(entry, 'Album')
genre = lookup(entry,'Genre')
count = lookup(entry, 'Play Count')
rating = lookup(entry, 'Rating')
length = lookup(entry, 'Total Time') if name is None or artist is None or album is None or genre is None:
continue print(name, artist, album, genre, count, rating, length) cur.execute('''INSERT OR IGNORE INTO Artist (name)
VALUES ( ? )''', ( artist, ) )
cur.execute('SELECT id FROM Artist WHERE name = ? ', (artist, ))
artist_id = cur.fetchone()[0] cur.execute('''INSERT OR IGNORE INTO Album (title, artist_id)
VALUES ( ?, ? )''', ( album, artist_id ) )
cur.execute('SELECT id FROM Album WHERE title = ? ', (album, ))
album_id = cur.fetchone()[0] cur.execute('''INSERT OR IGNORE INTO Genre (name)
VALUES ( ? )''', ( genre, ) )
cur.execute('SELECT id FROM Genre WHERE name = ? ', (genre, ))
genre_id = cur.fetchone()[0] cur.execute('''INSERT OR REPLACE INTO Track
(title, album_id, genre_id, len, rating, count)
VALUES ( ?, ?, ?, ?, ? ,?)''',
( name, album_id, genre_id, length, rating, count ) ) conn.commit()

《Using Databases with Python》Week3 Data Models and Relational SQL 课堂笔记的更多相关文章

  1. 《Using Databases with Python》 Week2 Basic Structured Query Language 课堂笔记

    Coursera课程<Using Databases with Python> 密歇根大学 Week2 Basic Structured Query Language 15.1 Relat ...

  2. 【Python学习笔记】Coursera课程《Using Databases with Python》 密歇根大学 Charles Severance——Week4 Many-to-Many Relationships in SQL课堂笔记

    Coursera课程<Using Databases with Python> 密歇根大学 Week4 Many-to-Many Relationships in SQL 15.8 Man ...

  3. 《Python Data Structures》Week5 Dictionary 课堂笔记

    Coursera课程<Python Data Structures> 密歇根大学 Charles Severance Week5 Dictionary 9.1 Dictionaries 字 ...

  4. 《Python Data Structures》 Week4 List 课堂笔记

    Coursera课程<Python Data Structures> 密歇根大学 Charles Severance Week4 List 8.2 Manipulating Lists 8 ...

  5. 潭州课堂25班:Ph201805201 python 模块json,os 第六课 (课堂笔记)

    json 模块 import json data = { 'name':'aa', 'age':18, 'lis':[1,3,4], 'tupe':(4,5,6), 'None':None } j = ...

  6. Mongodb Manual阅读笔记:CH3 数据模型(Data Models)

    3数据模型(Data Models) Mongodb Manual阅读笔记:CH2 Mongodb CRUD 操作Mongodb Manual阅读笔记:CH3 数据模型(Data Models)Mon ...

  7. 《Using Databases with Python》Week1 Object Oriented Python 课堂笔记

    Coursera课程<Using Databases with Python> 密歇根大学 Charles Severance Week1 Object Oriented Python U ...

  8. 数据分析---《Python for Data Analysis》学习笔记【04】

    <Python for Data Analysis>一书由Wes Mckinney所著,中文译名是<利用Python进行数据分析>.这里记录一下学习过程,其中有些方法和书中不同 ...

  9. 数据分析---《Python for Data Analysis》学习笔记【03】

    <Python for Data Analysis>一书由Wes Mckinney所著,中文译名是<利用Python进行数据分析>.这里记录一下学习过程,其中有些方法和书中不同 ...

随机推荐

  1. hdu 6205 card card card 最大子段和

    #include<iostream> #include<deque> #include<memory.h> #include<stdio.h> #inc ...

  2. 【NOIP2013模拟】水叮当的舞步

    题目 水叮当得到了一块五颜六色的格子形地毯作为生日礼物,更加特别的是,地毯上格子的颜色还能随着踩踏而改变. 为了讨好她的偶像虹猫,水叮当决定在地毯上跳一支轻盈的舞来卖萌~~~ 地毯上的格子有N行N列, ...

  3. 【leetcode】1186. Maximum Subarray Sum with One Deletion

    题目如下: Given an array of integers, return the maximum sum for a non-empty subarray (contiguous elemen ...

  4. springboot(十)使用LogBack作为日志组件

    简介: 企业级项目在搭建的时候,最不可或缺的一部分就是日志,日志可以用来调试程序,打印运行日志以及错误信息方便于我们后期对系统的维护,在SpringBoot兴起之前记录日志最出色的莫过于log4j了, ...

  5. MYSQL安装失败,一打开就出现MySQL-Workbench已停止工作

    1.由于系统重新安装,环境都是新的,出现MySQL-Workbench已停止工作 解决:下载  微软常用运行库合集  安装即可

  6. POJ 3275 Ranking the cows ( Floyd求解传递闭包 && Bitset优化 )

    题意 : 给出 N 头牛,以及 M 个某些牛之间的大小关系,问你最少还要确定多少对牛的关系才能将所有的牛按照一定顺序排序起来 分析 : 这些给出的关系想一下就知道是满足传递性的 例如 A > B ...

  7. QT信号槽 中的对象野指针

    例: connect(&objec1,&class::slot_func1,&object2,&class::slot_func2) 如果 &objec   传 ...

  8. BZOJ 1022 Luogu P4279 [SHOI2008]小约翰的游戏 (博弈论)

    题目链接: (bzoj) https://www.lydsy.com/JudgeOnline/problem.php?id=1022 (luogu) https://www.luogu.org/pro ...

  9. HDU1429--胜利大逃亡(续)(BFS+状态压缩)

    Time Limit: 4000/2000 MS (Java/Others)    Memory Limit: 65536/32768 K (Java/Others)Total Submission( ...

  10. DVWA--XSS(反射型)

    0X01爱之初介绍 虽然XSS已经做了两节了 但是还是还是简单解释一下 前言:跨站脚本(Cross-Site Scripting,XSS)是一种经常出现在Web应用程序中的计算机安全漏洞,是由于Web ...