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

3. After that, you will add the ADD CONSTRAINT clause to specify that you are adding a constraint.

4. Then, you will give your constraint a name. This can be anything you like, but it should be descriptive of its purpose. For example, if you are adding a unique constraint to the 'email' column, you might name your constraint 'unique_email'. The syntax is as follows: ADD CONSTRAINT constraint_name

5. Finally, you will specify that this is a unique constraint and on which column it should be applied. The syntax is as follows: UNIQUE (column_name)

So, the complete SQL statement would look something like this:

ALTER TABLE table_name ADD CONSTRAINT constraint_name UNIQUE (column_name);

This statement will add a unique constraint to the specified column in the table, ensuring that no two rows can have the same value in this column.