Database FundamentalsLecture 4

Useful website for MySQL download

http://www.net-language.com/workshops/Default.asp?workshop=21

The Design Process

Good decisions require good information derived from raw

facts known as data.

Importance of good database design

• Well designed database facilitates data management and becomes a good information generator.

• It will grow well.• It is easy to use.

NoteNo

Packer Comp Comp Add

ItemNo

Qty PartNo Descrip

300 JW Bloggs York 1 200 1234 Nuts

300 JW Bloggs York 2 200 2234 Bolts

300 JW Bloggs York 3 200 3334 Nails

What is wrong with this organisation’s database?

Info about Packer, Comp and CompAdd has been repeated in more than one row

If Bloggs was the only company to have purchased Nuts and then decided they did not want them so were deleted from packing note, contents of ParNo and Descrip fields would be lost

PartNo and Descrip fields cannot be established until a packing note has been raised.

Update anomaly

Delete anomaly

Insert anomaly

Architect

Plan

Builder

House

Database Designer

Database Design

Database Builder

Database System

The Database Design Process

1 Define the current process.

2 Define the components of the organisation.

3 Define rules (how organisation is run).

4 Model the database.

5 Define the relationships.

6 Review.

7 Create the database.

4, 5, 6 & 7 are pertinent to this module.

Entities

Things it may be required to keepinformation about.Can be: People (e.g. Customers)

Objects (e.g. Products)happening (e.g.ad hits)

address14 Grand Ave59 Cucumber Dr928 Shingles Rd2572 Family Ave

phone01484-75293401274-84247201924-82417301246-474738

Company_num13141723

Company_nameBig Deal LtdPickles IncReal Roofing CoGigafred & Son

company

Company_num

142317132323231323141317

ad_num

484952556263647799

101102119

Hit_fee

0.010.020.010.030.020.010.020.030.030.010.010.02

product

dateJuly 13July 13July 14July 14July 14July 14July 14July 14July 14July 14July 14July 14July 14July 14July 15July 15July 15July 15

ad_num49554863

10162

119102524864

11948

10163487799

ad hits

Is it an entity?

Rules:1. An entity must be important to the

organisation.2. An entity must have at least one

attribute.3. An entity must occur more than once

(there must be more than one customer)4. Each entity occurrence (record) must be

uniquely identifiable (customer id)

Entities are represented like this and they are always singular.

customer

Bits of data associated with the entity are attributes:

Customer number

Customer name

Customer address

Contact name

Telephone

Way of identifying occurrence (record) - the primary key.

Relationships

customer invoice

product

Three types of Relationhip

• one-to-one (1:1)• one-to-many (1:M)• many-to-many (M:N)

car driver

car driver

car driver

car driver

1:1 A car can only have one driver; a driver can have only one car.

1:M A car can have more than one driver; a driver can only one car.

1:M A car can have only one driver; a driver can have more than one car.

M:N A car can have more than one driver; a driver can have more than one car.

A typical company

Managing

DirectorCompan

y

Sales Staff Customer

employs

manages

take orders

Relationship name

Sales Staff Customertake

orders

Sales Staff Customer

Order

accepts places

This many-to-many relationship does not enable mapping between a particular order and a particular member of the sales staff

The entity Order uniquely defines an instance involving both Sales Staff and Customer. From a single many-to-many relationship two one-to-many relationships have been created.

Sales Staff

Staffid

Name

DOB

Employ start date

Order

Orderid

Staffid*

Customerid*

Order details

Customer

Customerid

Name

Address

Contact name

Telephone

Foreign keys

A model is:

• Simplified abstractions of real world events or conditions.

• A database model is a collection of logical constructs used to represent the data structure and the data relationships within the database

• 2 categories of database models:– Conceptual models (what is presented)– Implementation models (how it is

represented)

Entity (E-R) Relationship Model

(top down approach)• A conceptual model and like other

conceptual models it uses three types of relationship:

• one-to-many (1:N)• one-to-one (1:1)• many-to-many (M:N) Multiplicity is a term which can be used todescribe this.

• ENTITY - is a person place or thing for which data are to be collected or stored e.g.student, book, author, stock

• ATTRIBUTE - characteristics of an entity e.g. student entity may include the attributes student number, date of entry, pathway, dob, home address, phone number etc.

• RELATIONSHIP - an association between entities e.g.

Week 4 practical

In week 4 you will be working with the 3 tables:

• book• author• stock

And you will make queries such as:

USE ;DROP TABLE IF EXISTS book;CREATE TABLE book(

bookid INT UNSIGNED NOT NULL AUTO_INCREMENT PRIMARY KEY,

title VARCHAR(50) NOT NULL,author VARCHAR(20) NULL,topic VARCHAR(20) NOT NULL,pages INT UNSIGNED NULL,firstPubDate YEAR NULL,publisher VARCHAR(40) NOT NULL,price FLOAT(4,2)

);

DROP TABLE IF EXISTS stock;CREATE TABLE stock(

bookid INT UNSIGNED NOT NULL,authorid INT UNSIGNED NOT NULL,reorder INT NOT NULL,instock INT NOT NULL

); DROP TABLE IF EXISTS author;CREATE TABLE author(

authorid INT UNSIGNED NOT NULL AUTO_INCREMENT PRIMARY KEY,

lastname VARCHAR(20) NOT NULL,firstname VARCHAR(20) NOT NULL

);

SELECT book.title, author.lastname, author.firstname, stock.instock

FROM book, author, stock WHERE stock.instock <5

AND stock.bookid=book.bookid AND stock.authorid=author.authorid ;

1) SELECT title FROM book \c ; 2) SELECT book.title, author.authorid FROM book, author \c ; 3) SELECT book.title, author.authorid, stock.instock FROM book, author, stock WHERE author.lastname='GLANCEY' AND author.authorid=stock.authorid \c ; 4) SELECT book.title, author.authorid, stock.instock FROM book, author, stock WHERE author.lastname='GLANCEY' AND author.authorid=stock.authorid AND stock.bookid=book.bookid \c ;  5) SELECT book.title, author.lastname, author.firstname, stock.instock FROM book, author, stock WHERE stock.instock <5 AND stock.bookid=book.bookid AND stock.authorid=author.authorid \c ;