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    Question

    Which of the following keys ensures that no duplicate

    values are allowed and also uniquely identifies a record in a relational database table?
    A Foreign Key Correct Answer Incorrect Answer
    B Composite Key Correct Answer Incorrect Answer
    C Primary Key Correct Answer Incorrect Answer
    D Alternate Key Correct Answer Incorrect Answer
    E Candidate Key Correct Answer Incorrect Answer

    Solution

    The primary key is a critical concept in database design. It uniquely identifies each record in a table and enforces entity integrity. 1. Uniqueness: A primary key ensures that each record in the table has a unique identifier, preventing duplicates. 2. Non-Null Constraint: The primary key field cannot contain null values, ensuring every record is identifiable. 3. Database Operations: Many database operations, such as joins and lookups, rely on the primary key for accurate and efficient processing. 4. Example: In a table of employees, the EmployeeID column can serve as a primary key to uniquely identify every employee. These properties make the primary key indispensable for maintaining data integrity. Why Other Options Are Incorrect: • A) Foreign Key: Establishes a relationship between two tables but does not ensure uniqueness within a table. • B) Composite Key: Comprises two or more columns to uniquely identify a record but is not a primary key unless explicitly defined. • D) Alternate Key: A candidate key not chosen as the primary key, used as an alternate unique identifier. • E) Candidate Key: Represents all fields that can qualify as primary keys but lacks the enforced selection of the primary key.

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