CIE IGCSE Computer Science
Revision Notes
IGCSEComputer ScienceCIERevision Notes9. Databases9.1 Database
TheoryDatabases
Databases
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Test Yourself
Single Table Databases
•
•
•
A database is a structured collection of data so it can be searched, sorted,
filtered and analysed quickly
o Data in a database can be any type of data including text, images,
videos, sound
Databases use tables to store data
Tables have records of data represented by one row
o In the example below, each row represents the data stored about a
single customer (the customer’s record)
o In the customer table there are 3 records
o Each record is divided into fields (CustomerID, FirstName, LastName,
DOB and Phone Number)
A Database Table Containing Customer Details
CustomerID FirstName LastName
•
DOB
PhoneNumber
1
Andrea
Bycroft
05031976
0746762883
2
Melissa
Langler
22012001
0756372892
3
Amy
George
22111988
0746372821
Fields are represented by the columns in a table
o There are 5 fields in the customer table
o The first row in a table contains the field names which is the heading
for the data stored in that field
o Each field in a table has a data type which defines what data can be
entered into that field
Worked example
A Database Table Containing Pet Details
DogID
Name
Breed
Age
Gender
DG12
Smokey
Poodle
12
M
DG34
Harvey
Springer Spaniel
10
M
DG48
Maisie
Labradoodle
3
F
DG49
Maggie
Labradoodle
3
F
DG88
Winston
Bulldog
7
M
DG95
Shona
Golden Retriever
6
F
How many fields are there in the Dogs table shown above?
[1]
5 [1]
How many records are there in the Dogs table?
[1]
6 [1]
Exam Tip
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It is very likely you will be presented with an example database table and
identify either how many fields there are or how many records there are so
make sure you remember a record is row and a field is a column
Validation and Verification
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Verification checks check whether the data that has been entered is
the correct data and is accurate
o This is often completed by getting data entered by one person is then
checked by another person
When a table is created, validation rules can be assigned to the different
fields
o A validation rule controls what data can be entered into that field
o There are different types of validation checks used to limit what data
can be entered into each field
The different types of validation check
Type
Description
Length
Check
This type of validation checks the number of characters that have been entered
into a field. For example, you might make phone numbers entered have to be
eleven characters long
Format This type of validation checks data entered meets an exact format. For example, a
Check
product code might have to be two letters followed by five numbers
Range
Check
A range check will check the number entered is within a specific range. For
example, the age of a dog would be between 0 - 40. Any other number would be
disallowed
Presence
Check
A presence check can be added to fields which cannot be left blank
Type
Check
A type check will allow data with a specific data type to be entered into a field. For
example, if text was entered into a field which is supposed to contain the date of
birth of a person it would not be allowed
Check digit validation is a process used to verify the accuracy of numbers such as
credit card numbers. A check digit is a single digit added to the end of the number,
Check
which is calculated based on a specific algorithm applied to the other digits in the
Digits
number. When the data is re-entered the same algorithm can be applied and if it
produces a different result the code is incorrect
Worked example
A Database Table Containing Student Grades
StudentID FirstName LastName MarkSubmitted
1483792
1498378
1500121
1382972
1598264
1548282
Shanay
Poppy
Diya
Joe
Anton
Felicity
Giles
Petit
Dinesh
Swaile
Smith
Hall
Y
N
Y
Y
Y
N
Percentage
55
20
74
68
34
47
Describe two validation checks that could be used to check data being inputted
into the table above
[4]
StudentID could have a length check to ensure 7 characters are entered [2]
FirstName and LastName could have a presence check to make a record cannot be
entered without entering the name of the student [2]
A type check of boolean could be applied to the Mark Submitted field so that only Y
or N are entered [2]
A range check could be assigned to the Mark column to ensure only numbers
between 0 and 100 are entered [2]
Data Types
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Table fields are represented by columns in a table
There are 5 fields in the customer table below
o These include CustomerID, FirstName, LastName, DOB and
PhoneNumber
A Database Table Containing Customer Details
CustomerID FirstName LastName
1
2
3
•
Andrea
Melissa
Amy
Bycroft
Langler
George
DOB
PhoneNumber
05031976
22012001
22111988
0746762883
0756372892
0746372821
Each field in a table, has a data type
o Common data types include text/alphanumeric, character, boolean,
integer, real and date/time
o Phone numbers have to be assigned the text/alphanumeric data type
because they begin with a 0
▪ If you assigned the data type Integer to a phone number it would
remove the initial 0
Database Data Types
Data Type
Text/Alphanumeric
Character
Boolean
Integer
Real
Explanation
Example
This data type allows letters, special characters like spaces and
NG321AE
punctuation and numbers to be entered into a field
This allows single characters to be entered into a field.
Characters can be any alphanumeric value and can be lowercase
A
or uppercase
This data type can be used in fields where there are only two
possible options. Data is stored as a 1 or 0 in the database but True/False
can be used to represent True/False or Yes/No
Only whole numbers can be entered
15
Numbers including decimal numbers can be stored
30.99
Date/Time
Only dates or times can be entered into a field with this type. A
format for the date/time can also be assigned to the field
180855
Worked example
A Database Table Containing Dog Details
DogID
Name
Breed
Age Gender
DG12 Smokey
Poodle
12
M
DG34
Harvey
Springer Spaniel
10
M
DG48
Maisie
Labradoodle
3
F
DG49
Maggie
Labradoodle
3
F
Bulldog
7
M
Golden Retriever
6
F
DG88 Winston
DG95
Shona
What data type should Age be?
[1]
Integer [1]
What data type should DogID be?
[1]
Text/Alphanumeric [1]
CIE IGCSE Computer Science
Revision Notes
IGCSEComputer ScienceCIERevision Notes9. Databases9.1 Database
TheoryPrimary Keys
Primary Keys
Primary Keys
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Each table has a primary key field which acts as a unique identifier
o Each item of data in this field is unique
Duplicate data items would be blocked if they were entered into the
primary key field
Because the items of data are unique within the primary key field they can be
used to identify individual records
o
•
A Database Table Containing Customer Details
CustomerID FirstName LastName
•
•
DOB
PhoneNumber
1
Andrea
Bycroft
05031976
0746762883
2
Melissa
Langler
22012001
0756372892
3
Amy
George
22111988
0746372821
In the example customer table, the primary key would be
the CustomerID because each customer’s ID is unique
If there was a customer with the same name they could be identified correctly
using the CustomerID
Worked example
A database table containing the details of dogs
DogID
DG12
DG34
DG48
DG49
DG88
DG95
Name
Smokey
Harvey
Maisie
Maggie
Winston
Shona
Breed
Poodle
Springer Spaniel
Labradoodle
Labradoodle
Bulldog
Golden Retriever
Age
12
10
3
3
7
6
Gender
M
M
F
F
M
F
Which field would be suitable for the primary key? Explain why
[2]
DogID [1]
It is a unique identifier [1]
It does not contain any duplicate data items [1]
CIE IGCSE Computer Science
Revision Notes
IGCSEComputer ScienceCIERevision Notes9. Databases9.2 SQLSQL
SQL
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Test Yourself
SQL
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•
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Records in a database can be searched and data can be manipulated
using Structured Query Language (SQL)
SQL statements can be written to query the data in the database and extract
useful information
SQL statements follow this structure:
o SELECT the fields you want to display
o FROM the table/tables containing the data you wish to search
o WHERE the search criteria
A Database Table Containing Movie Details
MovieID
Name
Genre
M23
Moana
Family
M8
Shaun of the Dead Comedy
M56
Die Hard
Action
M34
Big
Family
Example
Certificate Rating
U
18
18
PG
8.1
8.7
8.4
8.5
SELECT Name, Rating
FROM Movie
WHERE Rating>8.4;
The results of this query would be:
Name
Rating
Shaun of the Dead
Big
8.7
8.5
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The two fields - Name and Rating have been extracted from the Movie table
and then the records have been filtered by Rating
This example uses the > operator to search for records where the rating
is greater than 8.4
•
There are several other comparison operators which can be used to create
the filter criteria in the WHERE line of a SQL query
SQL Comparison Operators
Operator
Description
>
>=
<
<=
=
<>
Example
Greater than
Greater than or equal to
Less than
Less than or equal to
Equal to
Not equal to
SELECT Name,Rating
FROM Movie
WHERE Genre=”Family” AND Certificate=”U”;
The results of this query would be:
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Name
Rating
Moana
8.1
The two fields Name and Rating have been extracted from the Movie table
and the records have been filtered by both Genre and Certificate
This query uses the AND logical operator to include multiple criteria in the
WHERE line of the SQL query
Another logical operator which can be used in the WHERE statement is OR
o For example, WHERE Genre=”Comedy” OR Genre=”Family”
Worked example
A database table, Dogs2023, is used to keep a record of all dogs registered at a
veterinary practice
DogID
Name
Breed
Age
Gender
DG12
Smokey
Poodle
12
M
DG34
Harvey
Springer Spaniel
10
M
DG48
Maisie
Labradoodle
3
F
DG49
Maggie
Labradoodle
3
F
DG88
Winston
Bulldog
7
M
DG95
Shona
Golden Retriever
6
F
Complete the structured query language (SQL) to return the name and breed of all
Female dogs.
SELECT Name,Breed
________ Dogs2023
WHERE _______;
[2]
FROM [1]
Gender=”F” [1]
Write an SQL query to find out the name and breed of all dogs aged 10 years old or
older
[4]
SELECT Name, Breed [1]
FROM Dogs2023 [1]
WHERE Age>=10; [2]
ORDER BY
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You can enter a fourth line to the statement using the ORDER BY command,
followed by ASC or DESC
o If you enter ASC the results of the query will be sorted
in ascending order
o If you enter DESC the results of the query are sorted
in descending order
Example
SELECT Name,Genre, Certificate, Rating
FROM Movie
ORDER BY Name ASC
•
The results of this query would be:
Name
Genre
Certificate
Rating
Big
Die Hard
Moana
Shaun of the Dead
Family
Action
Family
Comedy
PG
18
U
18
8.5
8.4
8.1
8.7
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The query has returned four fields and all records because there were no
WHERE criteria. The records are sorted by Name alphabetically
o If numbers are sorted in ascending order they go from the lowest
number at the top of the table to the highest number at the bottom
o Descending order is the highest number to the lowest
SUM and COUNT commands
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The SUM command can be used to add numerical data
The COUNT command can be used to count items of data
ProductID
ProductName
Price
QuantityInStock
1
Sausages
1.99
3
2
Chips
2.99
2
3
Beans
2.50
5
4
Bananas
2.10
12
5
Avocado
1.00
3
Example
SELECT SUM(QuantityInStock)
FROM ProductTable;
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This query will add up all of the numbers in the QuantityInStock field
o The result of this query would be 25
Example
SELECT COUNT(*)
FROM ProductTable
WHERE Price>2;
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This query will count all the records with a price greater than 2
o The result of this query would be 3
o This is because there are three products with a price greater than £2
(Chips, Beans, Bananas)