证明两节点能正常failover的sql

select instance_name,host_name,NULL AS failover_type,NULL AS failover_method,NULL AS failed_over FROM v$instance UNION SELECT NULL,NULL,failover_type,failover_method,failed_over FROM v$session WHERE username='SYSTEM';
        此语句显示当前使用的节点名和实例名.再将此主机数据库实例关闭.
          再运行此sql语句,显示第二个节点的节点名和实例名.
        此测试证明两节点能正常failover.