Difficulty: Easy

Average Score: 100%

What is true of the data values contained in a primary key?

Rationale

A primary key cannot contain null or blank values.

A primary key is a unique identifier for a record in a database table. It must contain unique values for each record, ensuring that no two records can have the same key, which is essential for maintaining data integrity. Importantly, null or blank values are not permissible in a primary key, as they would compromise its ability to uniquely identify records.

A (It cannot contain name values) YOUR ANSWER

This statement is incorrect because a primary key can indeed include name values, provided that they are unique within the table. For example, a table may use a person's name as a primary key if no two records share the same name. The restriction on primary keys relates to uniqueness and the presence of null values, not the type of data they can contain.

B (It cannot contain null or blank values) CORRECT

This is the correct answer, as primary keys must always contain valid, non-null values to ensure that each record can be uniquely identified. Allowing null or blank values would violate the core principle of a primary key, which is to provide a reliable and distinct reference for every record in a database.

C (It cannot contain zero values) YOUR ANSWER

While it is technically possible for a primary key to contain zero values, it is generally discouraged unless zero is a valid and unique identifier in the context of the data. The main requirement for primary keys is uniqueness and the absence of null values, not the exclusion of specific numeric values like zero.

D (It cannot contain number values) YOUR ANSWER

This statement is also incorrect because primary keys can certainly consist of numeric values, as long as they are unique and not null. Many databases use integers or other numeric types as primary keys, such as auto-incremented IDs, which serve as efficient identifiers for records.

Conclusion

In summary, a primary key is a crucial aspect of database design, requiring unique, non-null values to effectively identify records. While it can consist of various data types, including numbers and names, the prohibition against null or blank values is essential to maintaining data integrity and enabling reliable access to records. Understanding these constraints is fundamental for anyone working with relational databases.

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