ORA-16633: the only instance of the database cannot be removed
Cause: The instance to be removed was the only instance of the corresponding database that was known to the broker.
Action: Remove the corresponding database object from the broker configuration instead of the individual instance object of the database.
ORA-16633错误表明，试图删除数据库时，当前实例中只有一个实例，无法删除该实例。官方解释如下：
ORA-16633: “Cannot drop/disable the only available instance”
Cause: An attempt was made to drop or disable the only instance of a database.
Action: either open another instance to the same database before performing this operation, or have a cold backup available if the attempt fails.
此错误常常出现在试图从Oracle实例或复制到数据库中删除最后一个实例时。正确处理此错误的步骤是：
1）先确定数据库中实例的数量；
2）如果数据库只有一个实例，则无法删除该实例；
3）要删除实例，必须先打开另一个实例；
4）最后，再从数据库中删除该实例。