def cohort(characteristics, options = {})
      select_manager = arel.clone
      select_manager.projections = []
      select_manager.where Strategy.create(select_manager, characteristics, options)
      select_manager
    end
def cohort(characteristics, options = {})
      select_manager = arel.clone
      select_manager.projections = []
      select_manager.where Strategy.create(select_manager, characteristics, options)
      select_manager
    end
@note This doesn't return a <code>ActiveRecord::Relation</code>, so you can't just call count.

 @example Count a Flight cohort
   cohort = Flight.cohort(:origin => 'MSN', :dest => 'ORD')
   cohort.count #=> BAD! just plain Arel::SelectManager doesn't provide #count, that's an ActiveRecord::Relation thing
   Flight.connection.select_value(cohort.project('COUNT(*)').to_sql) #=> what you wanted

 @return [Arel::SelectManager] A select manager without any projections.