1、ORA-12514 TNS：listener does not currently know of service requested in connectdescriptor.
This indicate:
The database service is not dynamically registered with the listener.OR,The database service name is not configured in the listener.ora file
2、ORA-12541:TNS:no listener
The listener is not running on the database specified in the connect descriptor .
3、ORA-03113:TNS:end-of-file on communication channel
The database is not open .
4 、ORA-12154：TNS:could not resolve the connect identifier specified.
The connect identifier supplied does not exist in the tnsnames.ora file
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