Key definition: is a key a set of one or more attributes that uniquely identifies a row (tuple) in a relation?

Introduction / Context:
Keys are central to relational design. This question checks the basic definition of a key in a relation and whether it uniquely identifies tuples.

Given Data / Assumptions:

• We consider candidate keys and the chosen primary key.
• A key can consist of one attribute or a combination (composite key).
• Uniqueness is the defining property; minimality defines a candidate key.

Concept / Approach:
A key is any minimal superkey: it uniquely identifies rows and no proper subset does. The statement focuses on uniqueness, which is correct. Whether a key is selected as the primary key is a naming and implementation choice; it does not affect the definition.

Step-by-Step Solution:

Verification / Alternative check:
In SQL, declare UNIQUE constraints (or PRIMARY KEY) to enforce uniqueness, reflecting the theoretical concept.

Why Other Options Are Wrong:

• “Incorrect” contradicts the fundamental definition.
• Limiting to primary key is unnecessary; all candidate keys uniquely identify rows.
• Numeric types are irrelevant; keys can be strings, dates, etc.

Common Pitfalls:
Confusing “primary key” (one chosen key) with the general concept of “key” (candidate keys).

Final Answer:
Correct