Relational databases: table

The idea

This row is a table header fragment from section 3.7.1, not a full question. Treat it as a prompt to reason about how a relational database is organised into tables. A table stores records of one kind of thing, with each column holding one field and each row holding one record. A primary key is a field that uniquely identifies each record in its table, and a foreign key is a field in one table that refers to the primary key of another, linking the tables. When a multiple-choice item asks you to pick the correct description, test each option against these definitions: does the key uniquely identify records, and does the link point to another table's primary key? Choose the option that matches the definition exactly rather than the one that merely sounds technical.

What earns the marks

• A table stores records of a single kind of thing, with columns as fields and rows as records.
• A primary key is a field whose value uniquely identifies each record within its table.
• A foreign key is a field in one table that refers to the primary key of another table, creating a link between them.
• Relational databases reduce duplication by storing data in related tables linked by keys rather than repeating data in one large table.
• When selecting an option, match it precisely to the definition of table, primary key or foreign key rather than choosing on the basis of technical-sounding wording.

Common mistakes and how to put them right

• Confusing primary and foreign keys.

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

• Describing a table as a single record.

  Put it right: A table holds many records, with each row being one record.

• Choosing an option because it uses impressive vocabulary rather than checking it against the definition of the key or table being asked about.

Exam tips

• Read the stem to see whether it asks about a table, a primary key or a foreign key, then apply that exact definition to each option.
• Eliminate options that swap the roles of primary and foreign keys before comparing the remaining choices.
• Check the chosen option against a concrete example, such as a student table linked to a course table by a course identifier.