The 2nd Hand Student Book Database Jon HavierHigh Distinction Assignment, Autumn 2007

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Introduction to the 2nd hand Student Book Database 2nd Hand Student book database simulates a DMS currently

in use by Student Exchange, an online website that exchanges contact details for students to sell their books.

www.textbookexchange.com.au 2nd Hand student book is a simplified version It aims to create a nexus between sellers and buyers

advertised by both parties through certain criteria’s such as book title, edition and location.

This is a website familiar with many university students and helps in the purchase of course textbooks which can be very expensive

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Student Exchange Website

www.textbookexchange.com.au

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The ERD for 2nd Hand student books Database

2nd Hand student Books – 4 tables

Sale table is a weak entity as its primary key is borrowed from Student and textbook table

Entities and Relationships

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1:Many relationship

1:Many relationship (1:m) occurs when one record in a table is related to multiple records in another table. An example would be one student can sell many textbooks while one textbook can only belong to one student.

Therefore the seller table has a 1:m relationship with the Textbook table.

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1:Many relationship One Student can buy many textbooks (ISBN)

Studentemail other columns

10000000@student.uts.edu.au

…

… etc … …

Studentemail ISBN Addate

10000000@student.ut s.edu.au

9789470811481

01/01/2007

10000000@student.uts.edu.au

9263738492713

01/01/2007

Foreign key

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M:M relationship

M:M relationship occurs when one record in a table is related to multiple records in another table and vice-versa. An example would be one student email with many ISBN no’s and one ISBN with many student e-mail's.

Therefore a student table has a many to many (indirect) relationship with the Sale table

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One Studentemail can have many ISBN and one ISBN can have many Studentemail

M:M relationship

Studentemail ISBN Addate etc10000000@student.uts.edu.au

9789470811481

01/01/2007

…

20000000@student.uts.edu.au

9789470811481

01/01/2007

…

10000000@student.uts.edu.au

9263738492713

01/01/2007

…

20000000@student.uts.edu.au

9263738492713

01/01/2007

…

SQL Queries SQL query 1: Simple Query of a single tableSQL query 2: Natural JoinSQL query 3: Cross productSQL query 4: Group BySQL query 5: Sub-querySQL query 6: Cross product (Self join)

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SQL query 1 – Simple SELECT

A Select statement allows the database user to select and view a number of columns in a table or many tables with certain specific criteria. The output of the query depends on the selected columns, the tables required and the criteria applied to them.

SELECT ______ FROM____________ WHERE_______ HAVING __________ GROUP BY____________ Etc.________ ;

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SQL query 1 - Simple Show ISBN & Selleremail of all

textbooks registered SELECT ISBN, Selleremail FROM

Jontext2007textbook;

ISBN | Selleremail --------------+-------------------------------------------- 9789470811481 | 10000001@student.uts.edu.au Etc (15 rows)

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SQL query 2 – Natural Join

A natural join combines two or more tables via a common column.

The primary key of one table matches the foreign key of another table

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SQL query 2 – Natural Join Display ISBN, selleremail, sellerphone & sellername of all sellers

currently selling the textbook with ISBN: 9789470811481

Select ISBN, selleremail, sellerphone, sellername from Jontext2007textbook natural join Jontext2007seller

where ISBN = 9789470811481 ;

ISBN | Selleremail |Sellerphone | Sellername

--------------+-----------------------------+-------------+--------- 97894708114| 10000001@student.uts.edu.au | 0400000001 | Alberto (1 row)

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SQL query 3 – Cross Product Version Essential a natural join but

database users define the join specifically. Used for more complex joins

Using dot format, a database user will specifically detail the columns which will be joined

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SQL query 3 – Cross Product Version

Display ISBN, selleremail, sellerphone & sellername of all sellers currently selling the textbook with ISBN: 9789470811481 in Cross-product form

Select ISBN, selleremail, sellerphone, sellername from Jontext2007textbook T1, Jontext2007seller T2Where T1.Selleremail = T2.Selleremail AND ISBN = 9789470811481 ;

ISBN | Selleremail |Sellerphone | Sellername

-------------------+----------------------------+-------------+------- 9789470811481 | 10000001@student.uts.edu.au| 0400000001 | Alberto (1 row)

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SQL query 4 – Group By

A group by in a table is a function that allows certain data in a table to be collapsed into one row based on a column with the same variable

Having: Similar to WHERE Uses aggregate functions in a query, having acts like a

‘where’ in determining the condition used

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SQL query 4 – Group By Show the student name which have more than one book for sale and

how many books they have for offer Select studentname, count (*) as Number_of_books from

Jontext2007student natural join Jontext2007Forsale group by StudentName having count (*) > 1;

Studentname | Number_of_books --------------+------------------------ Alberto | 3 Bob | 3 Cameron | 4 David | 3 (4 rows)

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SQL query 5 - Sub-query

Essentially a query within a query

Used to find often a single result

Often used for complex queries

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List ISBN, price of all textbooks where price is the highestSELECT ISBN, Price FROM Jontext2007textbook WHERE price >= ALL (Select price FROM Jontext2007textbook);

ISBN | Price --------------+-------------------------- 9789470811481 | 100 (1 rows)

SQL query 5 - Sub-query

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SQL query 6 – Self-join

A self join is another version of cross join where a table is joined to its self kin order to find different rows in the table with matching elements

Often for more complex queries

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Show the books (ISBN) which are available from the same seller

SELECT T1.Selleremail, T1.texttitle, T1.Author, T2.ISBN, T2.price FROM Jontext2007textbook T1, Jontext2007textbook T2 WHERE T1.selleremail = T2.Selleremail AND t1.ISBN < T2.ISBN;

Selleremail | Texttitle | Author | ISBN | Price --------------+----------------------------------- 100000001@stud| Aust. Accounting | Picker, L & Radford | 9789470811481 | $100 (1 rows)

SQL query 6 – Self-join

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CHECK Constraints Example

Check statements prevent database user from entering data which could corrupt and create inconsistency with the database or data making it not logical for its field

They include entering names into date fields which should be a numerical field

Avoids the possibility of Murphy’s Law ‘Things will go wrong in any given situation, if you give

them a chance’ – wiki

CHECK statements don’t give them that chance

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CREATE TABLE Jontext2007textbook

(

ISBN INTEGER NOT NULL, Selleremail VARCHAR (50) NOT NULL, Texttitle VARCHAR(100) NOT NULL, Author VARCHAR(300) NOT NULL, Edition VARCHAR(50) NOT NULL, University VARCHAR(50) NOT NULL, Subject VARCHAR(50) NULL, Price INTEGER NOT NULL,

CONSTRAINT PKtextbook PRIMARY KEY (ISBN), CONSTRAINT Price CHECK (Price > 0), CONSTRAINT University CHECK (University = 'UTS' OR University =

'UNSW' OR University = 'MACQ' OR University = 'UWS'), CONSTRAINT FKtextbook FOREIGN KEY (Selleremail) REFERENCES Jontext2007Seller ON DELETE CASCADE );

CHECK Constraints Example

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SQL Syntax for Actions

Action statements are measures used to prevent the corruption of data when there is a change or a deletion of one of the records in one table.

These actions correct the relating data in the other associated tables by using a ‘cascade’ effect

Again avoids the possibility of Murphy’s Law ‘Things will go wrong in any given situation, if you give

them a chance’ – wiki

Action statements don’t give them that chance

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SQL Syntax for Actions CREATE TABLE Jontext2007textbook

(

ISBN INTEGER NOT NULL, Selleremail VARCHAR (50) NOT NULL, Texttitle VARCHAR(100) NOT NULL, Author VARCHAR(300) NOT NULL, Edition VARCHAR(50) NOT NULL, University VARCHAR(50) NOT NULL, Subject VARCHAR(50) NULL, Price INTEGER NOT NULL,

CONSTRAINT PKtextbook PRIMARY KEY (ISBN), CONSTRAINT Price CHECK (Price > 0), CONSTRAINT University CHECK (University = 'UTS' OR University = 'UNSW' OR University

= 'MACQ' OR University = 'UWS'), CONSTRAINT FKtextbook FOREIGN KEY (Selleremail) REFERENCES Jontext2007Seller ON DELETE CASCADE );

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Creating a View

Views allow database users to view a result of a statement that is used frequently without having to re-write that statement every time that view is required.

This creates ease of usability, one of the benefits of a DMS system

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An Example of Creating a View

CREATE VIEW Expensivebook(Texttitle, Price, Sellername)AS SELECT Title, Expensiveprice, Expensiveseller FROM Jontext2007textbook, Jontext2007seller WHERE textbook.Selleremail = Seller.Sellername;

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An Example of Querying a View Query exactly as if a table

SELECT * FROM Expensivebook;

Title Expensiveprice Expensiveseller

Aust. Accounting Standards

100 Alberto

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The End

Any Questions?