Which property helps ensure a column has unique values within a table?

Which property helps ensure a column has unique values within a table?

• A. Primary key
• B. Foreign key
• C. Unique property
• D. Length property

Answer: (C)

The key idea is enforcing uniqueness on a column with a constraint designed for that purpose. A unique constraint ensures that every value in that column is distinct across the entire table, so no duplicates can appear. That directly answers the need to have unique values in that column. A primary key also guarantees uniqueness, but it serves as the main row identifier and typically cannot be null, which makes it broader and more restrictive than what’s required if you just want a single column to be unique. A foreign key is about linking rows between tables and doesn’t by itself enforce uniqueness on the local column. The length property controls how much data a value can store, not whether values are unique. So the best fit for ensuring a column has unique values is applying a unique constraint.

The key idea is enforcing uniqueness on a column with a constraint designed for that purpose. A unique constraint ensures that every value in that column is distinct across the entire table, so no duplicates can appear. That directly answers the need to have unique values in that column.

A primary key also guarantees uniqueness, but it serves as the main row identifier and typically cannot be null, which makes it broader and more restrictive than what’s required if you just want a single column to be unique.

A foreign key is about linking rows between tables and doesn’t by itself enforce uniqueness on the local column. The length property controls how much data a value can store, not whether values are unique.

So the best fit for ensuring a column has unique values is applying a unique constraint.