Resolved ORACLE Error "ORA-12514"

This is an oracle error "ORA-12514"
this error rise several things on this one of them are resolved

if windows SQL>set ORACLE_SID=DBNAME
linux SQL>export ORACLE_SID=DBNAME
SQL> conn scott/tiger
connected
SQL>conn scott/tiger@tnsname
ORA-12514: TNS:listener does not currently know of service requested in connect descriptor.

Many Solution over here..

1. check database service is up
2. tnsnames.ora file are db name is correctly input.
3.
SQL>show parameter service_names
NAME TYPE VALUE
------------------------------------ ----------- ------------------------------
service_names string orcl.oracleworld.com

if appear this output

then edit the tnsnames.ora

Before :

orcl =
(DESCRIPTION=
(ADDRESS=
(PROTOCOL=TCP)
(HOST=10.20.7.50)
(PORT=1521)
)
(CONNECT_DATA=
(SERVICE_NAME= orcl.oracleworld.com ) <<<<--------------this line is edited.
)
)

After :

orcl =
(DESCRIPTION=
(ADDRESS=
(PROTOCOL=TCP)
(HOST=10.20.7.50)
(PORT=1521)
)
(CONNECT_DATA=
(SERVICE_NAME= orcl.oracleworld.com ) <<<<--------------this line is edited.
)
)

Then reconnect the database.