title: When to split up tables in SQL?
body: <p>I'm relatively new to SQL and trying to teach myself and I'm having a hard time understanding when to keep a column and when to separate it into a new table. </p>
  
  <p>I was watching a lecture where the instructor had a 'Customer' table and one of the columns was 'City' and a lot of the customers were from the same city so the data was redundant. He then broke off 'City' into its own table but that didn't quite make sense to me.  </p>
  
  <p>For example, I'm creating a College Course DB and I noticed that certain columns in the 'Course' dimension are repeating very often (like credit hours). Should I break credit hours off into its own table where that table would only have a couple of rows? What does this accomplish? I would still have to use a foreign key to reference the same value for every new data entry so would it even save on storage or would it just be an unnecessary join?</p>
  
  <p>I have other columns as well like 'Days of Week', 'Location', 'Class Time' which also only have a few values that repeat often. Should those be broken off into their own separate tables or be left part of the Course table?</p>