Beginning Oracle SQL for Oracle Database 18c

Question

First question:

My lessons e-book is for 18c, when you go to Oracle, the only download for Windows 10 is 21c, does this matter?

Second question: I attempted to download 21c anyway, now I have an error code ORA-12154 when trying to go into SQL Plus. I have looked online and tried to understand what is being said to do. Unfortunately, this is the first time I have worked with Oracle and SQL Plus, hence the lack of understanding.

Answer 1

1-First qestion:

You may run into Compatibility issues Features and functionalities introduced in 21c might not be available in 18c Oracle offers archived downloads of older versions. search for "Oracle Database 18c"

2- Second question:

ORA-12154 is connection problem. here are ways to troubleshoot:

a- Check TNSNAMES.ORA:Locate this file (usually in Oracle's network/admin directory).

b- Verify the service name you're using exists and matches the database you want to connect to.

Ensure entries have correct host names, port numbers, and SIDs.

c- Open a command prompt and run lsnrctl status to check if the Oracle listener is running If not, start it

with lsnrctl start.

d- Use ping to test network connectivity and confirm your computer can communicate with the database

server. If ping fails, it is firewall issue.

e- Ensure the TNS_ADMIN environment variable points to the directory containing tnsnames.ora.

f- Double-check you're using the correct username and password for the database.

Hope this helps