Unecessary column in shopping cart article?

In the PHP mysql shopping cart article what is the reason for the cartId column?

create table cart
(
cartId int auto_increment not null,
cookieId varchar(50),
itemId int,
qty int,
primary key(cartId),
unique id(cartId)
);


It doesn't seem to have any function even though it is named the same as the cookies name(meaning the cookies name in the name/value pair).

cartID is the unique identifier for that row. there is no guarantee that cookie id will be unique.

Do you mean that every table should have a unique identifier as a basic rule? Because even if the cookie id is not unique, the "cartID" column in the cart table is never refered to in the rest of the script.