def self.delete_old_data start_ts,end_ts
    start_date = start_ts.strftime("%Y-%m-%d")
    end_date = end_ts.strftime("%Y-%m-%d")
    Schedule.delete_all "utc_air_date >= '#{start_date}' AND utc_air_date <= '#{end_date}'"
    ScheduleAttribute.delete_all "utc_air_date >= '#{start_date}' AND utc_air_date <= '#{end_date}'"
    return true
  rescue
    false
  end