title: ActiveRecord includes. Specify included columns
body: <p>I have model Profile. Profile has_one User. User model has field email. When I call</p>
  
  <pre><code>Profile.some_scope.includes(:user)
  </code></pre>
  
  <p>it calls</p>
  
  <pre><code>SELECT users.* FROM users WHERE users.id IN (some ids)
  </code></pre>
  
  <p>But my User model has many fields that I am not using in rendering. Is it possible to load only emails from users? So, SQL should look like</p>
  
  <pre><code>SELECT users.email FROM users WHERE users.id IN (some ids)
  </code></pre>