title: Database count column
body: <p>I have two tables:</p>
  
  <pre><code>"sites" has_many "users" 
  "users" belongs_to "sites"
  </code></pre>
  
  <p>Is it better that whenever a <strong>users</strong> got added to <strong>sites</strong> I added column called <strong>users_count</strong> in sites table and increment it by one. Or is doing a conditional count on users table the best way?</p>