title: Hierarchical Data - Nested Set Model: MySql
body: <p>I am just learning how to implement the Nested Set Model but still have confusion with a certain aspect of it involving items that may be part of multiple categories.  Given the example below that was pulled from <a href="http://articles.sitepoint.com/print/hierarchical-data-database" rel="noreferrer"><strong>HERE</strong></a> and mirrors many other examples I have come across...</p>
  
  <p><img src="https://i.stack.imgur.com/edBO2.png" alt="Hierarchical Data: Numbered Tree"></p>
  
  <p><img src="https://i.stack.imgur.com/H7Pp4.png" alt="Table"></p>
  
  <p>How do you avoid duplication in the DB when you add Apples since they are multi-colored (i.e. Red, Yellow, Green)?</p>