Databases (Copy)

IGCSE / O Level Computer Science Cheat Sheet
Topic: 9 – Databases

A structured collection of data stored in tables consisting of fields (columns) and records (rows)
Supports efficient storage, retrieval, and management of data

Term	Description
Field	Column in a table (e.g. Name, Age)
Record	Row in a table (e.g. one person’s data)
Table	Set of related records
Primary Key	Unique identifier for each record
Validation	Ensures data entered is sensible and accurate

Data Type	Description	Example
Text/String	Letters, words, numbers not used in math	“John”
Character	A single letter or symbol	‘A’
Integer	Whole numbers	27
Real	Decimal numbers	3.14
Boolean	TRUE or FALSE	TRUE
Date/Time	Dates and timestamps	01/01/2025

Used to query and manipulate data in databases.

SQL Keyword	Function
SELECT	Retrieves fields from a table
FROM	Specifies the table to use
WHERE	Filters records by condition
ORDER BY	Sorts the result set
COUNT()	Returns the number of matching records
SUM()	Adds all values in a field

1. Retrieve all data from a table

SELECT * FROM Students;

2. Retrieve specific fields

SELECT Name, Age FROM Students;

3. Filter results

SELECT * FROM Students WHERE Age > 16;

4. Sort results

SELECT * FROM Students ORDER BY Age DESC;

5. Count records

SELECT COUNT(*) FROM Students;

6. Sum values in a column

SELECT SUM(Marks) FROM Students;

Method	Purpose
Validation	Checks data is reasonable/correct format
Verification	Confirms data has been entered correctly

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