You are the database developer for a leasing company. Your database includes a table that is defined as shown here: CREATE TABLE Lease (Id Int IDENTITY NOT NULL CONSTRAINT pk_lease_id PRIMARY KEY NONCLUSTERED, Lastname varchar(50) NOT NULL, FirstName varchar(50) NOT NULL, SSNo char(9) NOT NULL, Rating char(10) NULL, Limit money NULL) Each SSNo must be unique. You want the data to be physically stored in SSNo sequence. Which constraint should you add to the SSNo column on the Lease table?