Beginner
Database Management Systems
Q38 / 100
What is a unique constraint?
Correct! Well done.
Incorrect.
The correct answer is B) A constraint ensuring all values in a column are distinct (allows one NULL unless combined with NOT NULL)
B
Correct Answer
A constraint ensuring all values in a column are distinct (allows one NULL unless combined with NOT NULL)
Explanation
UNIQUE constraint prevents duplicate non-NULL values. Unlike PRIMARY KEY, multiple UNIQUE columns are allowed per table, and they can accept NULL values (behavior varies by DBMS).
Progress
38/100