How to calculate the greater value of the average between has_many association in rails 3

Question

I am new in rails,

I Have a Profile table and profile history table. Profile has many profile history. Profile table has id and current_count column and profile history has profile_id, and count column

i want to calculate all the profiles which have current_count greater than the average of the count value of the respective profile history

How can i achieve this in rails 3.

Answer 1

The appropriate sql query is

SELECT p.id, MIN(current_count), AVG(ph.count)  
FROM profiles p
INNER JOIN profile_histories ph on p.id=ph.profile_id
GROUP BY ph.profile_id, p.id
HAVING MIN(current_count) > AVG(ph.count)

Lets construct the rails way:

Profile.joins(:profile_histories)
  .select('profiles.id, MIN(profiles.current_count), AVG(profile_histories.count)')
  .group('profile_histories.profile_id, profiles.id')
  .having('MIN(profiles.current_count) > AVG(profile_histories.count)')