Includes still result in second database query when using constrained column relationship

I'm trying to use includes

in a query to limit the number of subsequent database calls that are fired on rendering, but I also want the included calls to select a subset of columns from related tables. Specifically, I want to get a set of posts, their comments and just the name of the user who wrote each comment.

So I added

belongs_to :user

belongs_to :user_for_display, :select => "users.id, user.name", :class_name => "User", :foreign_key => "user_id"

      

        
        
        
      

    

to my comment model.

From the console when I do

p = Post.where(:id => 1).includes(comments: [:user_for_display])

      

        
        
        
      

    

I can see that the correct requests are firing:

SELECT posts.* FROM posts WHERE posts.id = 1
SELECT comments.* FROM comments comments.attachable_type = "Post" AND comments.attachable_id IN (1)
SELECT users.id, users.name FROM users WHERE users.id IN (1,2,3)

      

        
        
        
      

    

but call

p.first.comments.first.user.name

      

        
        
        
      

    

still results in a call to a full database load:

User Load (0.5ms)  SELECT `users`.* FROM `users` WHERE `users`.`id` = 11805 LIMIT 1
=> "John"

      

        
        
        
      

    

The link only p.first.comments

does not trigger a second request for comments. And if I include the full relation :user

instead :user_for_display

, the call to get the username does not trigger a second user request (but I would rather not load the full user record).

Can SELECT be used to limit fields in include?