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Session 8: Databases
Teaching Computing to GCSE Level with Python
Topics today
Databases theory
 Databases
 Using SQL
Programming in Python with sqlite
Programming warm up
(optional)
Task
Write a function to convert from pounds to euros that takes
two parameters, the number of pounds and the exchange
rate. The function will convert pounds to euros and return
the number of euros.
Extension
Write a main() function that will ask the user to enter the
number of pounds and the exchange rate and then will call
the function you wrote above and then output the answer.
From the specification
OCR
AQA
Candidates should be able to:
 know how to read and write data from an
external database in a way that is appropriate
for the programming language(s) used and
the problem being solved
(a) describe a database as a persistent
organised store of data
(b) explain the use of data handling software
to create, maintain and interrogate a
database.
(c) separation of data from applications and
why this is desirable
(d) describe the principal features of a DBMS
and how they can be used to create
customised data handling applications.
(e) understand the relationship between
entities and tables
(f) understand the components of a relational
database, such as tables, forms, queries,
reports and modules
 understand the basic concepts of a relational
database as a data store
 be able to explain the terms record, field,
table, query, primary key, relationship, index
and search criteria
 be able to create simple SQL statements to
extract, add and edit data stored in
databases
 have experience of using these SQL
statements from within their own coded
systems
 be able to use databases from within their
own web based applications
What is a database?
A database is a collection of related data, organised such that
efficient data processing may be carried out on the data
contained in it.
The software used to control access to the data is known as a
Data Base Management System (DBMS)
Relational Database
CarReg
Make
AB02ERT
AG51DRT
Model
Colour
Year
Peugeot 206
Silver
2002
Ford
Green
2001
Focus
A collection of tables similar to
the one above
Terminology Quiz – these are the
answers!
Field
Query
Table
Module
Report
Relationship
SQL
Primary Key
Index
Record
Entity
Form
Definitions (or clues) to follow
There are 10 questions – write down the terms
A unique field of a record which
is used to identify that record.
An object, person, event or
thing of interest of an
organisation about which data is
to be held
Setting criteria to extract
particular data from a database
A feature of database software
used to view and enter data
A collection of fields describing
one instance in a table
The name of a column of data
stored in a table
A feature of database software
used to produce output from a
database
The implementation of an entity
in a database
A link or association between
two entities.
Storage of an ordered list of key
values
A standard language used to
describe and query data in a
database.
Answers!
An Example Data Dictionary
for
Contact(Surname, FirstName, Title, Street, Town, PostCode, TelNo)
Attribute
Surname
First Name
Title
Data Type
Text
Text
Text
Field Size
25
15
6
Required? Format
Yes
No
Mr, Ms,
Yes
Street
Town
Post Code
Tel. No.
Text
Text
Text
Text
20
20
8
15
Yes
Yes
No
No
Mrs, Miss,
Dr, Rev
LLNN NNLL
(STD
Code)number
Relationship
A relationship is a link or
association between two
entities
Types of Relationship
One-to-one
Husband and Wife
Person and Guide Dog
One-to-many
Mother and Children
Borrower and Library book
Many-to-many
Student and Course
Film and Film Star
Entity - Relationship
Diagrams
one - to - one
one - to - many
many - to - many
Enitity-Relationship Diagrams
Blind Person
Guide Dog
Specify both degree and name of
relationship
Enitity-Relationship Diagrams
owns
Blind Person has
Guide Dog
The name of a relationship
helps to establish its degree
Enitity-Relationship Diagrams
Ward
Patient
The name of a relationship
helps to establish its degree
Enitity-Relationship Diagrams
Ward
holds/has
is
Patient
The name of a relationship
helps to establish its degree
Enitity-Relationship Diagrams
Ward
Patient
The name of a relationship
helps to establish its degree
Enitity-Relationship Diagrams
Patient
Enitity-Relationship
Diagrams
attacks
Patient
suffers from
has
Enitity-Relationship Diagrams
attacks
Illness
Patient
suffers from
has
Many-to-many relationship
Many to Many relationships

The tables that make up a relational
database cannot represent many-tomany relationships

A many-to-many relationship can be
removed by creating a link entity

The link entity’s identifier (primary key)
will often be made up of the original
entities’ identifiers
Removing many-to-many
 E.g. Student and course
STUDENT

COURSE
Create a link table
STUDENT
ENROL
COURSE
Removing many-to-many

Using the table notation
Student(StudentID, Surname, DOB)
Course(CourseID, CourseName, Level)

With the link table
Student(StudentID, Surname, DOB)
Course(CourseID, CourseName, Level)
Enrol(StudentID, CourseID)
QBE Example:
The query is applied to the student table:
Student Name
Student Number D.o.B.
Heathcote, R
12345
20/08/73 AB
M
Head, J
22433
13/02/73 CD
F
Hargrave, R
66688
13/09/54 AB
M
Daley, C
87656
24/12/72 AB
F
The result of the query is
Tutor Group Gender
Student Name Tutor Group
Daley, C
AB
Head, J
CD
3
7
Structured Query
Language
 A standard language used to extract data from
a database. More flexible and powerful than
QBE and database independent.
 Key commands for selecting data
 SELECT
 FROM
 WHERE
 ORDER BY
Structured Query Language
To create a table
CREATE TABLE
To insert data
INSERT INTO <TABLENAME> <FIELDS>
VALUES <CORRESPONDING VALUES>
Create Table
create table customer(
customerID integer,
firstName text,
lastName text,
dateOfBirth text,
primary key (customerID))
TASK: sqLite Browser
sqLiteBrowser is open source software that works with sqlite
It can be downloaded from here
We use it prior to using Python and sqLite3 to give some
familiarity with SQL first
It can be a bit ropey so write your SQL in a text file first! – and
then paste in.
Use Sqlite to test the examples on the next three slides then
experiment with different types of SELECT statement
Create Table
create table car(
carReg text,
make text,
model text,
yearOfReg integer,
primary key (carReg))
INSERT INTO
INSERT INTO car
(carReg, make, model, yearOfReg)
Values
("MF59 YXS","Hyundai","i20",2009)
SELECT.. FROM.. WHERE
SELECT CarReg, Make
FROM Car
WHERE YearOfReg=2009
BREAK
Python and sqlite3