Relational databases: Explain the concept of a relational database.

The idea

A relational database stores data in tables, called relations, where each row is a record about one entity and each column is a field (attribute) holding one type of value. Tables are linked by keys: a primary key uniquely identifies each record in its own table, and a foreign key in one table holds a primary-key value from another table, creating a relationship. This structure avoids unnecessary duplication, because shared data is stored once and referenced, and it lets you query across tables using SQL.

For example: A Student table keyed on StudentID can be joined to a Club table through a ClubID foreign key, so a student's club is recorded without repeating club details on every student row.

What earns the marks

• A relational database organises data into tables (relations) of rows (records) and columns (fields/attributes).
• A primary key uniquely identifies each record in a table and cannot be duplicated or null.
• A foreign key is a field in one table that references the primary key of another table, creating a link between the tables.
• Relationships between tables allow data to be combined, for example by joining tables on matching key values.
• Storing shared data once and referencing it by key reduces duplication and inconsistency.
• Data can be retrieved across related tables using queries such as SQL.

Common mistakes and how to put them right

• Thinking a relational database is a single flat table.

  Put it right by explaining it is a set of linked tables joined by keys.

• Confusing primary and foreign keys.

  Put it right: A primary key uniquely identifies a record in its own table, whereas a foreign key references another table's primary key.

• Assuming relationships are stored by copying whole rows between tables.

  Put it right: Relationships are created by matching key values, not by duplicating records.

Exam tips

• Define the key terms table, record, field, primary key and foreign key before explaining how they link.
• Use a short concrete example of two tables joined by a key to show the relationship.
• Link the structure explicitly to a benefit such as reduced duplication or easier querying.