Alter Table Category Add CategoryName VARCHAR (20) NULL
ConsTRAINT EXB_UNIQUE UNIQUE
Create a unique constraint
Right-click on the database relationship chart to include the constraint, and then select the Properties command from the shortcut menu. - or - Right click on the table designer to open the table designer in the table designer, then select the Properties command from the shortcut menu. Select the Index / Key tab. Select the "New" command. The name of the system allocation appears in the Index Name box. In the list of "column name", select the columns attached to the constraint. To attach constraints to multiple columns, select other columns in subsequent rows. Select "Create a Unique" check box. Select Constraint option.
