Relational Databases – GCSE Computer Science Edexcel Revision

Understanding Relational Databases

Relational databases are a type of structured database in which data is stored in related tables.
Each table in a relational database represents a collection of related data items.
These tables are made up of rows, which represent individual records, and columns, which represent attributes or characteristics of those records.
The term ‘relational’ refers to the relationship between the data items stored in different tables.

An important feature of relational databases is the use of keys. These are special fields that allow the database to maintain its relationships.
A primary key is a unique identifier for a record in a table. This can be something like a customer ID, a student number or a product code.
A foreign key is a field in one table that uniquely identifies a record in another table. Foreign keys are used to link tables together.

Relationships between tables can be one-to-one, one-to-many, or many-to-many.
A one-to-one relationship means that each record in one table corresponds to one record in another table.
A one-to-many relationship means that a record in one table can relate to multiple records in another.
A many-to-many relationship requires a third linking table, as each record in the first table can relate to multiple records in the second table and vice versa.

To interact with a relational database, you use a standardised language known as SQL, which stands for Structured Query Language.
With SQL, you can execute a variety of tasks such as creating tables, inserting data into tables, updating existing data, deleting data, or retrieving data from the database.

Normalisation is a methodology in relational databases used to minimise data redundancy and avoid data anomalies.
It involves the process of organising the data into tables so that the dependency on the primary key is upheld.

Relational databases offer many benefits, including data integrity, security, and flexibility.
They support ACID properties (Atomicity, Consistency, Isolation, Durability) which are crucial for maintaining the data integrity.
They have strong security features, allowing administrators to set up permissions and restrict access to certain data.
They offer flexibility in data retrieval and manipulation thanks to SQL, allowing you to perform complex queries.