Session 8: DatabasesTeaching Computing to GCSE Level with Python

Topics todayDatabases theory

Databases

Using SQL

Programming in Python with sqlite

Programming warm up (optional)TaskWrite 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.

ExtensionWrite 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 specificationOCR

Candidates should be able to:

(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

AQA

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

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

A collection of tables similar to the one above

CarReg Make Model Colour Year

AB02ERT Peugeot 206 Silver 2002

AG51DRT Ford Focus Green 2001

Terminology Quiz – these are the answers!

Field

Table

Report

SQL

Index

Entity

Query

Module

Relationship

Primary Key

Record

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 DictionaryforContact(Surname, FirstName, Title, Street, Town, PostCode, TelNo)

Attribute Data Type Field Size Required? FormatSurname Text 25 YesFirst Name Text 15 NoTitle Text 6 Yes Mr, Ms,

Mrs, Miss,Dr, Rev

Street Text 20 Yes

Town Text 20 YesPost Code Text 8 No LLNN NNLL

Tel. No. Text 15 No (STDCode)-number

Relationship

A relationship is a link or association between two entities

Types of Relationship

One-to-oneHusband and WifePerson and Guide Dog

One-to-manyMother and ChildrenBorrower and Library book

Many-to-manyStudent and CourseFilm and Film Star

Entity - Relationship Diagrams

one - to - one

one - to - many

many - to - many

Enitity-Relationship Diagrams

Specify both degree and name of relationship

Blind Person Guide Dog

Enitity-Relationship Diagrams

The name of a relationship

helps to establish its degree

Blind Person Guide Dogownshas

Enitity-Relationship Diagrams

Ward Patient

The name of a relationship

helps to establish its degree

Enitity-Relationship Diagrams

Ward Patientholds/has

is

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

Patientattacks

suffers fromhas

Enitity-Relationship Diagrams

attacks

suffers fromhas

PatientIllness

Many-to-many relationship

Many to Many relationships The tables that make up a relational

database cannot represent many-to-many 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 tableCreate a link table

STUDENT COURSEENROL

Removing many-to-many Using the table notation

Student(StudentID, Surname, DOB)

Course(CourseID, CourseName, Level)

With the link tableStudent(StudentID, Surname, DOB)

Course(CourseID, CourseName, Level)

Enrol(StudentID, CourseID)

QBE Example:

The query is applied to the student table:

The result of the query is

Student Name Student Number D.o.B. Tutor Group Gender

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

Student Name Tutor GroupDaley, C ABHead, J CD

Structured Query Structured Query LanguageLanguageA 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

37

Structured Query LanguageTo 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 BrowsersqLiteBrowser 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 INTOINSERT 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