这是用于回滚旧的已经提交过的事务的脚本。可用于在多用户模式中将UNDO（取消）功能嵌入到客户端－服务器应用程序中-This is for rolling back the old has already submitted the affairs of the scr ipt. Can be used in multi-user mode will UNDO (canceled) functions into client-server application procedures