Note.grouped_awards generates queries that don't use indexes

This method looks as following:

def grouped_awards
  notes = {}
                                              
  awards.select(:note).distinct.map do |note|
    notes[note.note] = where(note: note.note)
  end
                                              
  notes["thumbsup"] ||= Note.none
  notes["thumbsdown"] ||= Note.none
                                              
  notes
end

Here the "note" column is used to match notes with a given value, but this column isn't indexed.

As per http://performance.gitlab.net/dashboard/db/note-grouped_awards the timings usually don't seem too bad, except for an occasional spike: