Question 2

Primary key

A primary key is an identifier that references a column in a database table where each value is unique, ensuring that no two records can have the same value for that identifier.

A) Foreign key

A foreign key is an identifier used to create a relationship between two tables by referencing the primary key of another table. While it may refer to a unique value in the parent table, it can contain duplicate values in the table where it is defined, thus failing to meet the criterion of uniqueness within a single table.

B) Structured database

A structured database refers to a collection of data organized in a defined manner, typically using tables. This term does not specifically refer to any unique identifiers or columns, making it irrelevant to the question about unique values in a column.

C) Primary key

The primary key is the correct answer because it specifically designates a column in a table where every value is unique, ensuring that each record can be distinctly identified. This characteristic is a fundamental aspect of relational database design.

D) Relational database

A relational database is a type of database that structures data into tables that can be linked by relationships. While it may include primary keys, the term itself does not identify a single unique column; therefore, it does not answer the question regarding uniqueness of values in a specific column.

Conclusion

The primary key is the definitive answer as it encapsulates the requirement for a column to have unique values within a table. Other options, such as foreign keys and relational databases, do not address the uniqueness of values in a single column, confirming that they are not suitable answers.