Difficulty: Easy
Correct Answer: A primary key
Explanation:
Introduction / Context:
Every relation (table) should have a way to uniquely identify each row. This uniqueness requirement underpins keys, indexing, and referential integrity.
Given Data / Assumptions:
Concept / Approach:
A primary key is the designated candidate key that uniquely identifies each row. While a surrogate key is a common implementation of a primary key, it is not required specifically—natural keys can serve. Foreign keys and alternate keys are optional depending on relationships and additional uniqueness needs.
Step-by-Step Solution:
Verification / Alternative check:
Normalization theory and most DBMS tools expect a primary key for each base table to ensure integrity and support indexing.
Why Other Options Are Wrong:
Foreign key: Only required if the table participates as child in a relationship.
Alternate key: Useful but optional.
Surrogate key: One way to implement a primary key, but not mandatory.
Common Pitfalls:
Assuming every primary key must be surrogate; sometimes a stable natural key is better.
Final Answer:
A primary key
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