title: Validation with both uniqueness and index
body: <p>I know that validating by creating an index is foolproof, compared to adding the "uniqueness" keyword to a model.</p>
  
  <p>Is there value in having both an index and the "uniqueness". Or would that be a bad idea?</p>
  
  <p>user.rb:</p>
  
  <pre><code>validates :email, uniqueness: true
  </code></pre>
  
  <p>schema.rb</p>
  
  <pre><code>add_index "users", ["email"], name: "index_users_on_email", unique: true
  </code></pre>