title: When to use an auto-incremented primary key and when not to?
body: <p>I'm trying to figure out the "best practices" for deciding whether or not to add an auto-incrementing integer as the primary key to a table.</p>
  
  <p>Let's say I have a table containing data about the chemical elements. The atomic number of each element is unique and will never change.  So rather than using an auto-incrementing integer for each column, it would probably make more sense to just use the atomic number, correct?</p>
  
  <p>Would the same be true if I had a table of books?  Should I use the ISBN or an auto-incrementing integer for the primary key?  Or a table of employees containing each person's SSN?</p>