Question

Assume that in a relation, more than one attributes are eligible to be primary keys. Since there can only be 1 primary key, so what we will call the other key(s)?

• A. Foreign key
• B. Candidate key
• C. Composite key
• D. Super key

Hint:

Formula to remember:
\[ \text{Candidate Keys} = \text{Primary Key} + \text{Alternate Keys} \]
If alternate key is not in the options, the other eligible keys are simply Candidate Keys!

Answer 1

The Correct Option is B

Step 1: Understanding the Question:
The question describes a database table where multiple columns are uniquely capable of identifying tuples, making them eligible to be the primary key. It asks how we classify these eligible keys.

Step 2: Database Key Classification Definitions:
- Candidate Key: Any minimal set of attributes that can uniquely identify a record in a table. All attributes eligible to become a primary key are candidate keys.
- Primary Key: The single candidate key selected by the database administrator to uniquely identify tuples in a table.
- Alternate Key: The candidate keys that were not chosen as the primary key.

Step 3: Detailed Explanation:
- In the scenario where multiple columns are eligible to be primary keys (e.g., AadhaarNumber and StudentRollNo):
- All of these unique attributes are defined as Candidate Keys.
- Since only one primary key can be active per relation, we select one (e.g., StudentRollNo) as the Primary Key.
- The remaining unused eligible keys (e.g., AadhaarNumber) are alternate keys.
- Since "Alternate Key" is not listed among the choices, we classify the other eligible keys under their general parent group, which is Candidate Keys.

Step 4: Final Answer:
The attributes eligible to be primary keys are called Candidate keys.
Hence, option (B) is the correct choice.