Which constraint ensures that a column in a database has unique values?

Prepare for your SDET Interview with comprehensive flashcards and challenging multiple-choice questions. Each question is designed with hints and detailed explanations to ensure your success. Start your journey to mastering the SDET Interview today!

The UNIQUE constraint is designed to ensure that all values in a specified column are unique across the table. This means that no two rows can have the same value in that particular column, thus maintaining data integrity and preventing duplication within that column.

While the PRIMARY KEY constraint also ensures uniqueness, it has the added requirement that the column must contain no NULL values and uniquely identifies each record in the table. Therefore, while both UNIQUE and PRIMARY KEY enforce uniqueness, the UNIQUE constraint specifically addresses the need for unique values without requiring that the column consists of a primary identifier for the entire record.

The NOT NULL constraint is unrelated to uniqueness; it only ensures that a column cannot have NULL values but does not prevent duplicate values. The FOREIGN KEY constraint, on the other hand, is used to establish a relationship between tables and ensure referential integrity, but it does not enforce uniqueness within the column of the table it resides in.

Hence, focusing on the requirement for ensuring unique values, the UNIQUE constraint is the most appropriate choice.