how to convert complex nested join sql query into Active Record rails 3?

Question

I created a SQL query and ran it successfully. This query returns the record that has the last transaction_time in each group.

Select s.id, s.location_id 
From sales_transactions s 
    INNER JOIN (
        Select location_id, MAX(transaction_time) AS lastest 
        From sales_transactions 
        Group By location_id) s1 
ON s.location_id = s1.location_id     
   AND s1.lastest = s.transaction_time

I used ActiveRecord::Base.connection.execute to run above query successfully. Now, I want to convert this SQL query into Active Record query in Rails 3. I did searched many questions here, however, because of the aggregate function in my sub query I can't find the solution.

Answer 1

You could do:

SalesTransaction.select('id', 'location_id', 'max(transaction_time) AS lastest').group(:location_id)

or a little bit different but the same result (plus faster):

SalesTransaction.order(:transaction_time).group(:location_id)