Relational Databases and SQL — AQA GCSE Computer Science

A database stores data in an organised way. A relational database uses linked tables, and SQL is used to query it.

Database basics

• A database is an organised, persistent store of data.
• A flat-file database is a single table, which can lead to data redundancy (repeated data) and inconsistency.
• A relational database uses multiple linked tables, reducing redundancy and improving consistency.

Key terms

• Table — a collection of records about one type of thing (e.g. Students).
• Record (row) — all the data about one item.
• Field (column) — one attribute (e.g. Surname).
• Primary key — a field that uniquely identifies each record.
• Foreign key — a field that links to the primary key of another table, creating a relationship between tables.

SQL (Structured Query Language)

SQL is used to retrieve and manipulate data. Key statements:

• SELECT … FROM … WHERE — retrieve specific data. e.g. SELECT Name, Age FROM Students WHERE Age > 15
• ORDER BY — sort the results (ASC or DESC).
• Wildcards and LIKE — search for patterns (e.g. WHERE Name LIKE 'A%').
• INSERT INTO … VALUES … — add a new record.
• DELETE FROM … WHERE … — remove records.
• UPDATE … SET … WHERE … — change existing data.

You should be able to read, interpret and write SQL statements for given tables.

Exam tips

• Learn the structure: table → record → field, with primary and foreign keys.
• A relational database reduces redundancy compared with a flat file.
• Know the main SQL keywords (SELECT, FROM, WHERE, ORDER BY, INSERT, DELETE, UPDATE).
• Practise writing SELECT … FROM … WHERE queries for sample tables.