What SQL statement is used to add a unique constraint to a column?OptionsUNIQUECHECKCONSTRAINTPRIMARY KEY

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 will use the ALTER TABLE statement to modify the structure of the table. The syntax is as follows: ALTER TABLE table_name

3. After the ALTER TABLE statement, you will add the ADD CONSTRAINT statement. This is used to add constraints to the columns in the table. The syntax is as follows: ADD CONSTRAINT constraint_name

4. Finally, you will use the UNIQUE keyword to specify that you want to add a unique constraint to the column. The syntax is as follows: UNIQUE(column_name)

So, the complete SQL statement will 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 this constraint, and "column_name" with the name of the column where you want to add the unique constraint.