Primary Key versus Unique Constraint?

Question

I\'m currently designing a brand new database. In school, we always learned to put a primary key in each table.

I read a lot of articles/discussions/newsgroups posts

Answer 1

You should always have a primary key.

However I suspect your question is just worded bit misleading, and you actually mean to ask if the primary key should always be an automatically generated number (also known as surrogate key), or some unique field which is actual meaningful data (also known as natural key), like SSN for people, ISBN for books and so on.

This question is an age old religious war in the DB field.

My take is that natural keys are preferable if they indeed are unique and never change. However, you should be careful, even something seemingly stable like a persons SSN may change under certain circumstances.