Correct Option: B. Unique entries Detailed Explanation: A primary key is a fundamental concept in database design and management. It is a specific field (or a combination of fields) in a database table that is used to uniquely identify each record in that table. Here’s a step-by-step breakdown of why option B is the correct answer:

1. Definition of Primary Key:
2. A primary key must contain unique values for each record. This means that no two rows in the table can have the same value for the primary key field. This uniqueness is crucial for maintaining data integrity and ensuring that each record can be distinctly identified.
3. Purpose of a Primary Key:
4. The primary key serves as a unique identifier for records in a database. For example, in a table of students, a student ID could be used as a primary key because each student has a unique ID. This allows for efficient data retrieval and ensures that operations like updates and deletions can be performed on specific records without ambiguity.
5. Enforcement of Uniqueness:
6. Most database management systems (DBMS) enforce the uniqueness of primary keys automatically. When you define a primary key on a field, the DBMS will not allow any duplicate values to be entered into that field. This is a critical feature that helps prevent data anomalies.
7. Types of Data in Primary Keys:
8. While primary keys can be numeric, text, or a combination of both, the key characteristic is that they must be unique. Therefore, the type of data (text, numeric, etc.) is not what defines a primary key; rather, it is the uniqueness of the entries that is essential.

Why Other Options Are Incorrect:

• Option A: Text only:
• This option is incorrect because a primary key can contain any type of data, not just text. It can be numeric, alphanumeric, or even a combination of different types. The defining feature of a primary key is not the data type but the uniqueness of the entries.
• Option C: Duplicate values:
• This option is fundamentally incorrect. A primary key cannot have duplicate values. If a field allowed duplicate values, it would not be able to uniquely identify records, which is the primary function of a primary key. Allowing duplicates would lead to confusion and data integrity issues.
• Option D: Numeric value only:
• Similar to option A, this option is incorrect because it restricts the primary key to numeric values only. A primary key can be a string, a date, or any other data type, as long as the values are unique. The key aspect is not the type of data but the uniqueness of the entries.

Common Pitfalls:

• Confusing Primary Key with Foreign Key: A primary key uniquely identifies a record in its own table, while a foreign key is a field in one table that links to the primary key of another table. Understanding this distinction is crucial.
• Assuming All Unique Fields are Primary Keys: Not all unique fields are primary keys. A primary key must be defined explicitly, and it is the field that is used for identification purposes.

Revision Summary:

• A primary key must contain unique entries to identify records distinctly.
• It can be of any data type (text, numeric, etc.), but uniqueness is the key feature.
• Duplicate values are not allowed in primary keys, as they would compromise data integrity.
• Understanding the role of primary keys is essential for effective database design and management.