Hi, this is my first post, and I'm not sure if it should go in this topic or not, but here it goes. I was reading about unique keys and primary keys in Wikipedia, and it seems that a primary key is a special case of a unique key, in that a primary key cannot hold a NULL value.
I was wondering:
1) Why are unique keys called "unique keys"?
2) Why use a unique key when you can use a primary key?