Question

In a relation, if more than one attribute can have distinct values, such attributes are called ______.

• A. Primary Key
• B. Candidate Key
• C. Foreign Key
• D. Composite Key

Hint:

Remember: All Primary Keys are Candidate Keys, but not all Candidate Keys are selected as the Primary Key.
A relation can have multiple Candidate Keys but exactly one Primary Key.

Answer 1

The Correct Option is B

Step 1: Understanding the Question:
The question asks for the terminology used in a relational database management system to describe attributes that can uniquely identify a tuple (row) because they contain distinct, non-duplicate values across all records.

Step 2: Key Concepts:
- Relation: A structure resembling a table with rows (tuples) and columns (attributes).
- Candidate Key: An attribute, or a minimal set of attributes, that uniquely identifies any tuple in a relation. If a table has multiple columns with distinct values, each is considered a candidate key.
- Primary Key: Out of all the candidate keys, the database designer selects one primary key to uniquely identify the records. There can only be one primary key per table.
- Alternate Key: Candidate keys that are not selected as the primary key are known as alternate keys.
- Foreign Key: An attribute in one table that references the primary key of another table, used to link the two tables.
- Composite Key: A key that consists of multiple attributes to uniquely identify a tuple.

Step 3: Detailed Explanation:
- When designing a relational schema, we identify columns that have unique values for all rows (e.g., AadhaarNumber, RollNumber, or EmailId in a student table).
- Each of these columns has the potential to uniquely identify a row because the values are distinct.
- Any column (or set of columns) that can uniquely identify a row is defined as a Candidate Key.
- If more than one attribute possesses distinct values, all of them are candidate keys because they are all candidates to be chosen as the primary key of the relation.

Step 4: Final Answer:
Attributes in a relation that have distinct values and are capable of identifying tuples uniquely are called Candidate Keys.
Hence, option (B) is the correct choice.