CBSE Class 12 Sample Paper for 2024 Boards

Computer Science - Class 12
Solutions to CBSE Sample Paper - Computer Science Class 12

## d. A foreign key is an attribute whose value is derived from the primary key of another relation.

c. A candidate key that is not a primary key is a foreign key.

A key is an attribute or a set of attributes that can uniquely identify a tuple in a relation. There are different types of keys in a relational database, such as candidate key, primary key, and foreign key.

• A candidate key is a minimal set of attributes that can uniquely identify a tuple in a relation. There can be more than one candidate key for a relation, but each candidate key must be unique and irreducible.
• A primary key is one of the candidate keys that is chosen by the database designer to identify the tuples in a relation. A primary key must be unique, not null, and minimal.
• A foreign key is an attribute or a set of attributes in one relation that refers to the primary key of another relation. A foreign key establishes a link between two relations and enforces referential integrity.

Based on these definitions, we can analyze the given statements and find out which one is false.

• Statement a: Any candidate key is eligible to become a primary key. This statement is true , because any candidate key can be chosen as the primary key by the database designer, as long as it satisfies the properties of a primary key.
• Statement b: A primary key uniquely identifies the tuples in a relation. This statement is true , because this is the main purpose of a primary key.
• Statement c: A candidate key that is not a primary key is a foreign key. This statement is false , because a candidate key that is not a primary key is still a candidate key, and it does not necessarily refer to the primary key of another relation. A foreign key can be any attribute or set of attributes that matches the primary key of another relation, not just a candidate key.
• Statement d: A foreign key is an attribute whose value is derived from the primary key of another relation. This statement is true , because this is how a foreign key establishes a link between two relations.

So, the correct answer is c. A candidate key that is not a primary key is a foreign key.

#### Davneet Singh

Davneet Singh has done his B.Tech from Indian Institute of Technology, Kanpur. He has been teaching from the past 14 years. He provides courses for Maths, Science, Social Science, Physics, Chemistry, Computer Science at Teachoo.