Elegant PostgreSQL Group by for Ruby on Rails / ActiveRecord

Question

Trying to retrieve an array of ActiveRecord Objects grouped by date with PostgreSQL.

More specifically I\'m trying to translate the following MySQL query:

Answer 1

My solution:

def self.columns_list
   column_names.collect { |c| "#{table_name}.#{c}" }.join(",")
 end

 scope :selling, joins(:products).group(columns_list)

Simple and repeatable.