What SQL statement is used to add a unique constraint to a column?OptionsUNIQUEPRIMARY KEYCHECKCONSTRAINT

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. After that, you use the ADD CONSTRAINT statement to add the unique constraint. The syntax is as follows:

   ADD CONSTRAINT constraint_name

4. Then, you specify that you want to add a unique constraint by using the UNIQUE keyword. The syntax is as follows:

   UNIQUE(column_name)

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