temp_model_builder.rb

class TempModelBuilder
  def self.build(sql, size)
    final_table_name = "tmp_#{Digest::MD5.hexdigest(sql)}"
    
    clazz = Class.new(ActiveRecord::Base)
    clazz.table_name = final_table_name
    
    # do stuff to create & populate the table
    
    clazz
  end
end

# you can create as many of these as you want.
model1 = TempModelBuilder.build('select * from ...', 50)
model2 = TempModelBuilder.build('select * from ...', 50)

# do activerecordish things now
result = model1.joins(:whatever).count