关于sqlplus中出现"Connected to an idle instance"问题的处理：
该问题在如下文章中有解释：
How to Check the Environment Variables for an Oracle Process (文档 ID 373303.1)
如下是从该文章中摘录：
The most used application of this document is when dealing with the "Connected to an idle instance" scenario for a bequeath sysdba connection.
This error indicates that ORACLE_SID and ORACLE_HOME in the current session do not match the same environment variables that were used when the database is started (ORACLE_SID and ORACLE_HOME are the strings used to uniquely identify the shared memory segment of the instance when a connection is done).
Check the ORACLE_SID and ORACLE_HOME of the background process and compare them with the ones in the current session to find the mismatch.
该问题，Oracle ACS 惜总也有记录：http://www.xifenfei.com/5197.html