code: func GetMaxScheduleAtForMulticastGroup(db sqlx.Queryer, multicastGroupID uuid.UUID) (time.Time, error) {
  	ts := new(time.Time)
  
  	err := sqlx.Get(db, &ts, `
  		select
  			max(schedule_at)
  		from
  			multicast_queue
  		where
  			multicast_group_id = $1
  	`, multicastGroupID)
  	if err != nil {
  		return time.Time{}, handlePSQLError(err, "select error")
  	}
  
  	if ts != nil {
  		return *ts, nil
  	}
  	return time.Time{}, nil
  }
docs: // GetMaxScheduleAtForMulticastGroup returns the maximum schedule at timestamp
  // for the given multicast-group.