Oracle SQPLUS ERROR:ORA-12560: TNS:protocol adapter error.


When I tried to connect the oracle database with sysdba as below,

SQL>connect / as sysdba;

I get the ORA-12560: TNS:protocol adapter error.


When I install the program, I use the default database name orcl, but I set oracle_sid=demodb1 in an early command for the database connection as demonstrated in this video (I did not watch Part 1 of the video).


Reset oracle_sid=orcl.