What SQL statement is used to add a unique constraint to a column?OptionsCONSTRAINTPRIMARY KEYUNIQUECHECK

The SQL statement used to add a unique constraint to a column is UNIQUE.

Here is a step-by-step guide on how to do it:

1. First, you need to decide on which column you want to add the unique constraint. This should be a column where you want each row to have a unique value.

2. Next, you use the ALTER TABLE statement to modify the structure of the table. The syntax is as follows:

ALTER TABLE table_name

3. Then, you add the ADD CONSTRAINT clause to specify the name of the constraint and the UNIQUE keyword to indicate that this is a unique constraint. The syntax is as follows:

ADD CONSTRAINT constraint_name UNIQUE (column_name)

4. So, the complete SQL statement would look like this:

ALTER TABLE table_name
ADD CONSTRAINT constraint_name UNIQUE (column_name);

Replace table_name with the name of your table, constraint_name with the name you want to give to the constraint, and column_name with the name of the column where you want to add the unique constraint.

5. Finally, run the SQL statement in your database management system to add the unique constraint to the column.