code: func (db *Database) Unlisten(channel string) error {
  	if db.listener == nil {
  		return errors.New("You must create a new listener first, calling Listen(channel)")
  	}
  
  	if channel == "*" {
  		return db.listener.UnlistenAll()
  	}
  	return db.listener.Unlisten(channel)
  }
docs: // Unlisten executes `UNLISTEN channel`. Unregister function f, that was registered with Listen(channel ,f).