code: func AddDeviceToMulticastGroup(db sqlx.Execer, devEUI lorawan.EUI64, multicastGroupID uuid.UUID) error {
  	_, err := db.Exec(`
  		insert into device_multicast_group (
  			dev_eui,
  			multicast_group_id,
  			created_at
  		) values ($1, $2, $3)`,
  		devEUI, multicastGroupID, time.Now())
  	if err != nil {
  		return handlePSQLError(err, "insert error")
  	}
  
  	log.WithFields(log.Fields{
  		"dev_eui":            devEUI,
  		"multicast_group_id": multicastGroupID,
  	}).Info("device added to multicast-group")
  
  	return nil
  }
docs: // AddDeviceToMulticastGroup adds the given device to the given multicast-group.