I always thought the Primary Key meant one field...the ID you want to make Primary.

However, I just ran into some examples in a book. They were making all ID's in a table "Primary". (This was a MS-SQL type book, so they showed the cute little picture of the "key", etc) So it looked like they were making the foreign keys in the table "keyed" also.

What is the purpose of this? Or can I go back to the thinking that only the main id of the table is the Primary key?

thanks,
Dustin