title: Ruby on Rails activerecord find average in one sql and Will_Paginate
body: <p>I have the following model association: a student model and has_many scores.</p>
  
  <p>I need to make a list showing their names and average, min, max scores. So far I am using 
  student.scores.average(:score) on each student, and I realise that it is doing one sql per student. How can I make the list with one joined sql?</p>
  
  <p>Also how would I use that with Will_Paginate plugin? </p>
  
  <p>Thank you</p>