ORA-12154 TNS:could not resolve service name
You might have come accross this error when connecting to an Oracle server from an Oracle client. Oracle client will throw this error if it is unable to connect to the server by using the service name specified. This error actually means that Sql * Net is unable to recognize the host/service name specified in the connection Parameters.
Explanation about how sql * net client connects to the server:
The parameters that are required to connect to an Oracle server.
1. Username
2. Password
3. Service name/connection String
What is a service name ?
Service name specifies an entry in the tnsname.ora file. Each service name consists of hostname/ip address of the Oracle database server you want to connect, Port at which Oracle listener is working, the database instance you want to connect to, and the protocol you are using for the connection.