What's the best practice for primary keys in tables?

Question

When designing tables, I\'ve developed a habit of having one column that is unique and that I make the primary key. This is achieved in three ways depending on requirements

Answer 1

I avoid using natural keys for one simple reason -- human error. Although natural unique identifiers are often available (SSN, VIN, Account Number, etc.), they require a human to enter them correctly. If you're using SSNs as a primary key, someone transposes a couple of numbers during data entry, and the error isn't discovered immediately, then you're faced with changing your primary key.

My primary keys are all handled by the database program in the background and the user is never aware of them.