title: modeling many to many unary relationship and 1:M unary relationship
body: <p>Im getting back into database design and i realize that I have huge gaps in my knowledge.</p>
  
  <p>I have a table that contains categories. Each category can have many subcategories and each subcategory can belong to many super-categories.</p>
  
  <p>I want to create a folder with a category name which will contain all the subcategories folders. (visual object like windows folders) 
  So i need to preform quick searches of the subcategories. </p>
  
  <p>I wonder what are the benefits of using 1:M or M:N relationship in this case?
  And how to implement each design?</p>
  
  <p>I have create a ERD model which is a 1:M unary relationship. (the diagram also contains an expense table which stores all the expense values but is irrelevant in this case)  </p>
  
  <p><img src="https://i.stack.imgur.com/myr6R.jpg" alt="1:M unary relationship"></p>
  
  <p>is this design correct?</p>
  
  <p>will many to many unary relationship allow for faster searches of super-categories and is the best design by default? </p>
  
  <p><strong>I would prefer an answer which contains an ERD</strong></p>