ct the correct answerWhat SQL statement is used to add a unique constraint to a column?OptionsUNIQUECHECKPRIMARY KEYCONSTRAINT

To add a unique constraint to a column in SQL, you use the UNIQUE keyword. This constraint ensures that all values in a column are distinct, meaning no duplicates are allowed. Here’s why the other options are not correct:

1. CHECK: This constraint is used to limit the values that can be placed in a column based on a specified condition but does not enforce uniqueness.

2. PRIMARY KEY: This constraint combines the unique constraint with the not-null constraint, meaning that it must contain unique values and cannot contain NULL. While a primary key does ensure uniqueness, it is specifically used for defining the primary identifier for a table.

3. CONSTRAINT: This is a generic term used for defining various types of constraints in SQL, including unique constraints, but it is not the specific keyword to apply a unique constraint on its own.

Final Answer

The correct answer is UNIQUE.