1. 19 – Databases: Multiple Tables

2. Session Aims & Objectives
To add dealing with multiple tables to your understanding of databases
Objectives, by end of this week’s sessions, you should be able to:
identify duplicated data in a single table
split that table to reduce data redundancy
generate SQL statements to (temporarily) join tables, and use these in your code

3. Flat files: Data Duplication
Field
Track
Track Title
Artist Name
Country
Paranoid
Black Sabbath UK
Falling in Love
Aerosmith US
Pink
Love in an Elevator
Smooth Criminal
Alien Ant Farm
Meaning of Life
Disturbed
The Game
Voices
Down with the Sickness
Record

4. Problem: Data Duplication
takes up lots of space
can become inconsistent (misspellings)
difficult to change (need to change each instance)
difficult to search (misspellings)

5. Relations (tables) Primary Key Foreign Key Track Track Title Artist ID
Paranoid 1
Falling in Love 2
Pink
Love in an Elevator
Smooth Criminal 3
Meaning of Life 4
The Game
Voices
Down with the Sickness
Artist
Artist ID
Artist Name
Country 1
Black Sabbath UK 2
Aerosmith US 3
Alien Ant Farm 4
Disturbed
Primary Key
Foreign Key

6. Normalisation Part of database design Process of breaking data down
Codd
7 stages of normalisation
Mathematical
Difficult to apply stages
Most professionals do it instinctively

7. Question: Prescriptions
Identify duplication and separate:
Prescription
Date
Surname
Forenames
Drug Name
6 Jan 04
Jones
Alison
Co-codamol
11 Jan 04
Smith
Bob
Tegretol
18 Jan 04
Hope
John
5 Feb 04
Johnson
Sally
8 Feb 04
10 Feb 04
Sorbitol

8. Question: Solution Patient PatientID Surname Forenames 1 Jones Alison2
Smith
Bob 3
Hope
John 4
Johnson
Sally
Prescription
Date
PatientID
DrugID
6 Jan 04 1
11 Jan 04 2
18 Jan 04 3
5 Feb 04 4
8 Feb 04
10 Feb 04
Drug
DrugID
Drug Name 1
Co-codamol 2
Tegretol 3
Sorbitol

9. People Database (with Hobbies)
Person ID
Surname
Forenames
Phone 1
Dixon
Mark 2
Smith
John 3
Jones
Sally 4
Bloggs
Fred 5
Anderson
Genny
Hobby
HobbyID
Description
PersonID 1
Archery 2
Herpetology 3
Music 4
Football 5
Rugby 6
Hitting people with swords

10. Entity-relationship diagrams
Each table in db
stores details of entity
shown as rectangular box
Person
Hobby
Relationships between tables
represent relationships between entities
shown as line between entities (boxes)

11. Relationship Types One-to-one One-to-many Many-to-one Many-to-many
(can't be implemented in relational database) A B A B A B A B

12. Question: Which relationship type?
Person ID
Surname
Forenames
Phone 1
Dixon
Mark 2
Smith
John 3
Jones
Sally 4
Bloggs
Fred 5
Anderson
Genny
Hobby
HobbyID
Description
PersonID 1
Archery 2
Herpetology 3
Music 4
Football 5
Rugby 6
Hitting people with swords
Person
Hobby

13. SQL: Joining tables SELECT * FROM [Person], [Hobby]; Two tables
Cartesian set
(all record
combinations):

14. SQL: Joining tables
Two tables
SELECT * FROM [Person], [Hobby] WHERE [Person].[ID] = [Hobby].[PersonID];
Matching records ID
Surname
Forenames
Phone
HobbyID
Description
PersonID 1
Dixon
Mark
Archery 2
Herpetology 3
Music 6
Hitting people with swords
Smith
John 4
Football 5
Rugby

15. SQL: Joining tables
SELECT [ID], [Surname] FROM [Person], [Hobby] WHERE [Person].[ID] = [Hobby].[PersonID]; ID
Surname 1
Dixon 2
Smith

16. SQL: DISTINCT records
SELECT DISTINCT [ID], [Surname] FROM [Person], [Hobby] WHERE [Person].[ID] = [Hobby].[PersonID]; ID
Surname 1
Dixon 2
Smith

17. SQL: More Loads more: Have a look at: group by
aggregate functions: average, count
inner joins
outer joins (left and right)
Have a look at:

18. Tutorial Exercise: Music
Task 1: Create the Music database (from the lecture) with the Track and Artist tables.
Task 2: Create a web page to display a list of Artists.
Task 4: Change that web page, so that each artist name is a link to another page, which displays all the tracks by that artist Hint: Use query strings to pass the artist ID between pages.

19. Tutorial Exercise: Prescriptions
Task 1: Create the Prescription database (from the lecture) with the Prescription, Patient, and Drug tables.
Task 2: Create a web page to display a list of Drugs.
Task 3: Change that web page, so that each drug name is a link to another page, which displays all the people using that drug.