KUP-11506：cannot change cluster in the same session\n

错误原因：An attempt was made to change the cluster in the same session. The first access to an Oracle BigData external table within a database session establishes the cluster for that session. This is determined by the cluster specified in the table's access parameters or, if no cluster was specified in the table's access parameters, by the default cluster set in the Oracle Big Data configuration file. Accessing an Oracle BigData external table in a different cluster within the same database session is not allowed.