1. IGCSE 4 Cambridge Designing a database table Computer Science
Section 2
Designing a database table
Unit 8
System design and databases 4

2. Objectives
To discuss some of the many computer systems which may hold data about you or your family on a database
To learn how this data is held so that information can be quickly retrieved
To learn some database terms: record, field, table, primary key, index
To set up a simple table in Access and enter some records

3. Who holds data about you or your family?
From the day you are born, someone holds data about you!
What about when you start school?
When you go to the doctor or the dentist?
When you join a Sports Club or some other organisation?
Does your family own a TV, a car, or buy things online?

4. ? What other data types are held?
An entity is a category of person or physical thing about which data is held in a database
What entities do these organisations hold data about?
A supermarket
A cinema
A Job Centre
A secondary school ?

5. Database structure A database contains one or more tables
A table has rows, each row containing one record
Columns in the table each contain one field of each record

6. A Film database The screenshot shows a database about films
The database has a single table with rows (records) and columns (fields)

7. MS Access database software
MS Access is a Database Management System (DBMS)
The TblFilm table was created using MS Access
This software allows you to create new tables, input and validate data, query the database and produce reports
Using Access you can create a customised application

8. Structure of a database table
Each field (or attribute) in the table has to be given a name and a data type

9. Creating and amending a table structure
When you create a new database table, you need to specify what type of data is to be stored in each field
Data types include:
Text,
integers,
real numbers with a decimal point,
dates,
currency, and
Yes/No fields

10. Choosing data types Data Example Data Type Age 14 Integer Shoe Size
6.5
Float
Price
14.99
Date of Birth
Height in CM
Quantity in Stock
Telephone Number

11. Choosing data types - Answers
Attribute
Example
Data Type
Age 14
Integer
Shoe Size
6.5
Float
Price
14.99
Currency or Real
Date of Birth
20/06/1992
Date
Height in CM
192 or 192.5
Integer or Real
Quantity in Stock 7
Telephone Number
001 (910)
Text

12. The primary key field
One field in the database has to be designated as the primary key
Each record in the table must have a different value in the primary key field
It uniquely identifies the record
Which field is the primary key field in the TblFilm table?

13. Indexing a field The primary key field is automatically indexed
You can specify that other fields are to be indexed
For example, you could specify that the field Title is to be indexed
In a very large database, this will speed up searches on that field, just like having an index at the back of a book

14. Worksheet 1 Complete Task 1 to add some records to the Films database
Complete Task 2 to change the structure of the database table

15. Validating fields
In order to minimise errors when data is entered into the database, as many fields as possible should be validated
This means specifying a rule that the data must obey
Validation rules include range checks, type checks, presence checks, format checks, list checks

16. Types of validation Range check: e.g. price must be between £1 and £25
Type check: e.g. A field must be a number data type
Presence check: Data must be entered in the field
Format check: e.g. Data must be in the format dd-mm-yy, or be an integer, or a valid postcode
List check: Data must be one of the items on a predefined list

17. Worksheet 1
Now try Task 3 on the Worksheet