title: Questions about types in MySQL
body: <p>So I was creating a table for comments, and I was wondering. What would be a good type for comment details? I put longtext. Well then, why would people need varchar if longtext can handle it? Also, which type would I want for usernames?</p>
  
  <p>What is the purpose of "primary" for index? What is the purpose of index?</p>
  
  <p><strong>Update:</strong>
  Let's say a comment was actually a review.</p>