csci/cmpe 4341 topic: programming in python chapter 10: database application programming interface...

CSCI/CMPE 4341 Topic: CSCI/CMPE 4341 Topic: Programming in PythonProgramming in Python

Chapter 10: Database Application Chapter 10: Database Application Programming InterfaceProgramming Interface

Xiang Lian

The University of Texas – Pan American

Edinburg, TX 78539

[email protected]

1

Objectives

• In this chapter, you will:– Understand relational database model

– Learn basic database SQL queries

– Use packages to create and query a database

2

Introduction

• A database is an organized collection of data• A database management system (DBMS)

provides mechanisms for storing, organizing, retrieving and modifying data

• Existing DBMSs–Microsoft SQL Server– Oracle– Sybase– IBM DB2

3

Introduction (cont'd)

• PostgreSQL and MySQL are popular open-source DBMSs that can be downloaded and used freely by anyone

• Microsoft’s free SQL Server Express, which is installed with Visual Studio, can be also downloaded separately from Microsoft (www.microsoft.com/express/sql)

4

Relational Database

• A relational database organizes data simply in tables– rows (also called records)

– columns (also called fields, attributes)• Primary key: a column (or group of columns) requiring

a unique value that cannot be duplicated in other rows

• A primary key composed of two or more columns is known as a composite key

• Foreign key—a column in this table that matches the primary-key column in another table

5

Example of Table: Employees

6

SQL

• A program might select data from the table to create a query result – E.g., to retrieve the location of each department, in

increasing order by Department number

– SQL: • SELECT DISTINCT Department, Location

FROM Employees

ORDER BY Department

7

SQL Results

8

Schema

• A database may contain one or multiple tables

• A database’s tables, their fields and the relationships among them are collectively known as a database schema

9

Entity-Relationship Model

• Entity-Relationship (ER) model– Entity• Authors

• Titles

– Relationship• There is a one-to-many relationship between a primary

key and a corresponding foreign key– E.g., one author can write many books and one book can be

written by many authors

• Others: many-to-many or one-to-one relationship

• E.g., AuthorISBN10

11

Example of Relational Database: Books Database

• Books database has four tables: Authors, Publishers, AuthorISBN and Titles

• Authors table has three fields: author’s unique ID number, first name and last name

• Publishers table has two fields: publisher’s unique ID and name

• AuthorISBN table has two fields: authors’ ID numbers and corresponding ISBN numbers

• Titles has seven fields: ISBN number, title, edition number, copyright year, publisher’s ID number, book price and filename of cover image

Example of ER Diagram

12

AuthorISBN

AuthorID

ISBN

Authors

AuthorID

FirstName

LastName

Publishers

PublisherID

PublisherName

Titles

ISBN

Title

EditionNumber

Copyright

PublisherID

ImageFile

Price

1 • 1

•

1

•

Authors Table

13

Field DescriptionAuthorID Author’s ID number in the database. In the Books database, this int field is defined as an

auto-incremented field. For each new record inserted in this table, the database increments the AuthorID value, ensuring that each record has a unique AuthorID. This field is the table’s primary key.

FirstName Author’s first name (a string).

LastName Author’s last name (a string).

Fig. 17.3 Authors table from Books.

AuthorID FirstName LastName1 Harvey Deitel

2 Paul Deitel

3 Tem Nieto

4 Kate Steinbuhler

5 Sean Santry

6 Ted Lin

7 Praveen Sadhu

8 David McPhie

9 Cheryl Yaeger

10 Marina Zlatkina

11 Ben Wiedermann

12 Jonathan Liperi

13 Jeffrey Listfield

Fig. 17.4 Data from the Authors table of Books.

Publishers Table

14

Field DescriptionPublisherID The publisher’s ID number in the database. This auto-

incremented int field is the table’s primary-key field.

PublisherName The name of the publisher (a string).

Fig. 17.5 Publishers table from Books.

PublisherID PublisherName1 Prentice Hall2 Prentice Hall PTGFig. 17.6 Data from the Publishers table of

Books.

AuthorISBN Table

15

Field DescriptionAuthorID The author’s ID number, which allows the database to

associate each book with a specific author. The integer ID number in this field must also appear in the Authors table.

ISBN The ISBN number for a book (a string).Fig. 17.7 AuthorISBN table from Books.

AuthorID ISBN AuthorID ISBN1 0130895725 1 01302841811 0132261197 1 0130895601

1 0130895717 2 0130895725

1 0135289106 2 0132261197

1 0139163050 2 0130895717

1 013028419x 2 0135289106

1 0130161438 2 0139163050

1 0130856118 2 013028419x

1 0130125075 2 0130161438

1 0138993947 2 0130856118

1 0130852473 2 0130125075

1 0130829277 2 0138993947

1 0134569555 2 0130852473

Titles Table

16

Field DescriptionISBN ISBN number of the book (a string).Title Title of the book (a string).EditionNumber Edition number of the book (a string).Copyright Copyright year of the book (an int).PublisherID Publisher’s ID number (an int). This value must

correspond to an ID number in the Publishers table.ImageFile Name of the file containing the book’s cover image (a

string).Price Suggested retail price of the book (a real number).

[Note: The prices shown in this database are for example purposes only.]

Fig. 17.9 Titles table from Books.

ISBN Title Edition-Number

Publish-erID

Copy-right

ImageFile Price

0130923613 Python How to Program 1 1 2002 python.jpg $69.95

0130622214 C# How to Program 1 1 2002 cshtp.jpg $69.95

0130341517 Java How to Program 4 1 2002 jhtp4.jpg $69.95

0130649341 The Complete Java Training Course 4 2 2002 javactc4.jpg $109.95

0130895601 Advanced Java 2 Platform How to Program 1 1 2002 advjhtp1.jpg $69.95

0130308978 Internet and World Wide Web How to Program

2 1 2002 iw3htp2.jpg $69.95

0130293636 Visual Basic .NET How to Program 2 1 2002 vbnet.jpg $69.95

0130895636 The Complete C++ Training Course 3 2 2001 cppctc3.jpg $109.95

17

Structured Query Language (SQL)

SQL keyword DescriptionSELECT Selects (retrieves) fields from one or more tables.FROM Specifies tables from which to get fields or delete records.

Required in every SELECT and DELETE statement.WHERE Specifies criteria that determine the rows to be retrieved.INNER JOIN Joins records from multiple tables to produce a single set of

records.GROUP BY Specifies criteria for grouping records.ORDER BY Specifies criteria for ordering records.INSERT Inserts data into a specified table.UPDATE Updates data in a specified table.DELETE Deletes data from a specified table.Fig. 17.12 SQL query keywords.

SQL on Books Database

• SELECT * FROM tableName– SELECT * FROM Authors

– SELECT AuthorID, LastName FROM Authors

• SELECT columnName1, columnName2, … FROM tableName WHERE criteria– SELECT Title, EditionNumber, Copyright

FROM Titles

WHERE Copyright > '2014'

18

SQL on Books Database (cont'd)

• Operator LIKE is used for pattern matching– Wildcard character

• Percent (%): zero or more characters

• Underscore (_): a single wildcard character

– SELECT AuthorID, FirstName, LastName

FROM Authors

WHERE LastName LIKE 'D%'

– SELECT AuthorID, FirstName, LastName

FROM Authors

WHERE LastName LIKE '_y%'

19

Deitel

Ayer

SQL on Books Database (cont'd)

• SELECT columnName1, columnName2, … FROM tableName ORDER BY column ASC– ASC– DESC– SELECT AuthorID, FirstName, LastName FROM Authors ORDER BY LastName DESC

• Other statements in SQL– table1 INNER JOIN table2 ON table1.columnName=table2.columnName– INSERT INTO tableName (columnName1, columnName2, … ) VALUES (value1,

value2, …)– UPDATE tableName SET columnName1 = value1, columnName2 = value2, …

WHERE criteria– DELETE FROM tableName WHERE criteria

20

2002 Prentice Hall.All rights reserved.

Outline21

Fig. 17.22 TitleAuthor query of Books database

1 SELECT Titles.Title, Titles.ISBN, Authors.FirstName, 2 Authors.LastName, Titles.Copyright, 3 Publishers.PublisherName4 FROM 5 ( Publishers INNER JOIN Titles 6 ON Publishers.PublisherID = Titles.PublisherID ) 7 INNER JOIN 8 ( Authors INNER JOIN AuthorISBN 9 ON Authors.AuthorID = AuthorISBN.AuthorID ) 10 ON Titles.ISBN = AuthorISBN.ISBN11 ORDER BY Titles.Title

22

Python DB-API Specification

• Python Database Application Programming Interface (DB-API): document that specifies common object and method names for manipulating any database

• Describes a Connection object that accesses the database

• Cursor object, created by Connection object, manipulates and retrieves data

• Three methods for fetching rows of a query result set – fetchone, fetchmany and fetchall

Pypyodbc: https://code.google.com/p/pypyodbc/

import pypyodbc

pypyodbc.win_create_mdb('C:\\Python34\\Books.mdb')

connection_string = 'Driver={Microsoft Access Driver (*.mdb)};DBQ= C:\\Python34\\Books.mdb'

connection = pypyodbc.connect(connection_string)

SQL = 'CREATE TABLE saleout (id COUNTER PRIMARY KEY,product_name VARCHAR(25));'

connection.cursor().execute(SQL).commit()

23

Example of Using pyodbc Packagehttp://en.wikibooks.org/wiki/Python_Programming/Dat

abase_Programming

import pyodbc DBfile = '/data/MSAccess/Music_Library.mdb'conn = pyodbc.connect('DRIVER={Microsoft Access Driver (*.mdb)};DBQ='+DBfile)#use below conn if using with Access 2007, 2010 .accdb file#conn = pyodbc.connect(r'Driver={Microsoft Access Driver (*.mdb, *.accdb)};DBQ='+DBfile)cursor = conn.cursor() SQL = 'SELECT Artist, AlbumName FROM RecordCollection ORDER BY Year;'for row in cursor.execute(SQL): # cursors are iterable print row.Artist, row.AlbumName # print row # if print row it will return tuple of all fields cursor.close()conn.close()

24

25

Database Query Example

• Presents a CGI program that performs a simple query on the Books database and displays result set in an XHTML table


Outline26

fig17_27.py

#!c:\python\python.exe# Fig. 17.27: fig17_27.py# Displays contents of the Authors table,# ordered by a specified field. import MySQLdb # for Python 2.X, MySQLdb does not support Python 3import cgiimport sys def printHeader( title ):

print ("""Content-type: text/html

<?xml version = "1.0" encoding = "UTF-8"?> <!DOCTYPE html PUBLIC"-//W3C//DTD XHTML 1.0 Transitional//EN""DTD/xhtml1-transitional.dtd"><html xmlns = "http://www.w3.org/1999/xhtml"xml:lang = "en" lang = "en"><head><title>%s</title></head> <body>""" % title) # obtain user query specificationsform = cgi.FieldStorage() # get "sortBy" valueif form.has_key( "sortBy" ):

sortBy = form[ "sortBy" ].valueelse:

sortBy = "firstName" # get "sortOrder" valueif form.has_key( "sortOrder" ):

sortOrder = form[ "sortOrder" ].valueelse:

Contains classes and functions for manipulating MySQL databases

Obtain form data

Get “sort by” value for ORDER BY

Get sorting order for ORDER BY


Outline27

fig17_27.py

sortOrder = "ASC" printHeader( "Authors table from Books" ) # connect to database and retrieve a cursortry:

connection = MySQLdb.connect( db = "Books" )

# error connecting to databaseexcept MySQLdb.OperationalError, error:

print ("Error:", error)sys.exit( 1 )

# retrieve cursorelse:

cursor = connection.cursor() # query all records from Authors tablecursor.execute( "SELECT * FROM Authors ORDER BY %s %s" %

( sortBy, sortOrder ) ) allFields = cursor.description # get field namesallRecords = cursor.fetchall() # get records # close cursor and connectioncursor.close()connection.close() # output results in a tableprint ("""\n<table border = "1" cellpadding = "3" > <tr bgcolor = "silver" >""") # create table headerfor field in allFields:

print ("<td>%s</td>" % field[ 0 ] )

Create Connection object to manage connectionSpecify database as value of keyword db

MySQLdb.connect failure raises MySQLdb.OperationalError exception

Create Cursor object

Execute query against database

Attribute description contains information about fieldsObtain all records

Close Cursor objectClose Connection object

Output results in table


Outline28

fig17_27.py

print ("</tr>") # display each record as a rowfor author in allRecords:

print ("<tr>")

for item in author:print ("<td>%s</td>" % item)

print ("</tr>")

print ("</table>" ) # obtain sorting method from userprint ("""

\n<form method = "post" action = "/cgi-bin/fig17_27.py">Sort By:<br />""" )

# display sorting optionsfor field in allFields:

print ("""<input type = "radio" name = "sortBy"value = "%s" />""" % field[ 0 ] )print (field[ 0 ])print ("<br />" )

print ("""<br />\nSort Order:<br />

<input type = "radio" name = "sortOrder"value = "ASC" checked = "checked" />Ascending<input type = "radio" name = "sortOrder"value = "DESC" />Descending<br /><br />\n<input type = "submit" value = "SORT" /></form>\n\n</body>\n</html>""" )

Display each record as a table row

Print form to obtain sorting information from user

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