What does Uniqueness ensure in a data collection?

What does Uniqueness ensure in a data collection?

• A. Requires each real-world instance to be represented only once in the data collection.
• B. Every column must have unique values.
• C. The data must be encrypted.
• D. Records must be stored in ascending order.

Answer: (B)

Uniqueness means preventing duplicates for a given attribute. In a data collection, you enforce uniqueness so that each value in a column appears at most once. This is done with a UNIQUE constraint on the column. The statement that every column must have unique values captures this idea, applying the constraint across all attributes to ensure no two rows share the same value in any column. For example, enforcing uniqueness on a user_id column guarantees you won’t have two records for the same user. The other options don’t describe this mechanism: encryption isn’t about duplicates, storing records in ascending order isn’t about uniqueness, and representing each real-world instance only once is a broader notion rather than the precise constraint used to enforce unique values in attributes.

Uniqueness means preventing duplicates for a given attribute. In a data collection, you enforce uniqueness so that each value in a column appears at most once. This is done with a UNIQUE constraint on the column. The statement that every column must have unique values captures this idea, applying the constraint across all attributes to ensure no two rows share the same value in any column. For example, enforcing uniqueness on a user_id column guarantees you won’t have two records for the same user. The other options don’t describe this mechanism: encryption isn’t about duplicates, storing records in ascending order isn’t about uniqueness, and representing each real-world instance only once is a broader notion rather than the precise constraint used to enforce unique values in attributes.