What should be set on a CDT to ensure the database generates a unique ID when inserting a new row?

To ensure the database generates a unique ID when inserting a new row, the correct approach is to use the option that specifies auto-generating the primary key. This method instructs the database to automatically create a unique identifier for each new record, which is essential for data integrity and relational database management.

By utilizing the auto-generate feature for the primary key, each new entry is assigned a unique value without requiring manual input, reducing the risk of duplicates and errors. This is particularly important in environments where multiple users or processes may be inserting data simultaneously, as it ensures that each record remains distinct and traceable.

The other options suggest alternative methods for ID assignment that do not rely on the database's inherent capability to generate unique IDs for new records, which may lead to issues with uniqueness or increased manual overhead. Therefore, setting the primary key to auto-generate is the most efficient and reliable method for ensuring unique identifiers in a database.