A Level Computer Science: Databases — Practice Questions (Cambridge 9618)

These are original questions written for Marlbridge, for revision and practice on this content. They are not reproduced past-paper questions, and they do not replicate the exam’s exact structure, question count or mark tariffs — Cambridge International holds copyright in its own papers. Use these alongside the official past papers available from your board.

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Questions

1. Define the terms candidate key and foreign key. [2]

2. Explain what is meant by referential integrity. [2]

3. State what is meant by a table being in first normal form (1NF). [1]

4. A table STUDENT has the fields StudentID, Name, Year and Tutor. Write an SQL statement to display the Name of every student in Year 12, in alphabetical order of Name. [3]

5. Explain the difference between a data definition language (DDL) and a data manipulation language (DML), giving one SQL command for each. [2]

Answers

1. A candidate key is an attribute (or smallest set of attributes) that could uniquely identify every record in a table; one candidate key is chosen as the primary key [1]. A foreign key is an attribute in one table that is the primary key of another table, used to link the two tables [1].

Examiner insight (June 2025): some candidates did not understand what a candidate key is, and a few gave primary keys when foreign keys were asked for. The primary key is also not always the first attribute listed in a table. Try the real question next: Cambridge International AS & A Level Computer Science 9618, June 2025, Paper 11, Question 5.

2. Every foreign key value must match an existing primary key value in the linked table [1], so a record cannot refer to a record that does not exist (for example, it cannot be deleted while records still refer to it) [1].

3. There are no repeating groups of attributes: every field holds a single (atomic) value and each record is unique [1].

4. SELECT Name [1] FROM STUDENT WHERE Year = 12 [1] ORDER BY Name; [1]

5. DDL is used to create and change the structure of a database, for example CREATE TABLE [1]; DML is used to add, change, delete or retrieve the data, for example SELECT, INSERT or UPDATE [1].

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Where marks are usually lost

• Giving the primary key when the question asks for a foreign key.
• Assuming the primary key is the first field in a table.
• Leaving out ORDER BY or putting the condition in the wrong clause.