Detailed explanation and options for the selected question.
What does the UNIQUE constraint ensure in a table?
A.
All values in a column are different
B.
A column cannot contain NULL values
C.
A column has a default value
D.
A column is referenced by another table
Explanation:
The UNIQUE constraint ensures all values in a column are different. Option B describes NOT NULL, Option C describes DEFAULT, and Option D relates to FOREIGN KEY.