Database Fundamentals — Question 121

Which constraint ensures a unique value in the ID column for each customer?

Answer options

• A. DISTINCT
• B. FOREIGN KEY
• C. SEQUENTIAL
• D. PRIMARY KEY

Correct answer: D

Explanation

The PRIMARY KEY constraint is specifically designed to ensure that each value in the ID column is unique for every customer, which is essential for identifying records. The DISTINCT option is used in queries to return unique values but does not enforce uniqueness at the database level. FOREIGN KEY is used to establish a relationship between two tables, and SEQUENTIAL is not a standard constraint in SQL.