title: One true Lookup table advantages vs. disadvantages
body: <p>So I've read enough to know that having one lookup table isn't the best way to go.  From a performance standpoint, why is that?  Consider the following example:</p>
  
  <p>you have a list of schools in cities.  There can me more than one school in a given city.
  So you have a junction table schoolCities between the two.  Now consider a list of businesses.  there can be more than one business in each city.  So you have a junction table businessCities.  The question really is: why is it so bad if you just use one cities table and make a junction table for schools and business versus having each table school and business its own copy of the cities table?  </p>