文档解释
ORA-56726: Category string is referred to by a consumer group and cannot be deleted
Cause: An attempt was made to delete a category that is referred to by a consumer group.
Action: Modify or remove all consumer groups that use this category and then retry.
ORA-56726：该错误表明存在消费组引用一个字符串分类，而无法删除该字符串类别。
官方解释
常见案例
一般处理方法及步骤
第一步：查看消费组的名称，确认该字符串分类被哪个消费组引用。
第二步：使用 DBMS_STREAMS_ADM.DROP_CONSUMER_GROUP 将消费组删除，或者用 DBMS_STREAMS_ADM.DROP_CATEGORY 将字符串分类以及相关消费组删除。
第三步：重试原来的删除分类操作，如果此时成功，表示上述操作已经解决了 ORA-56726 错误。
