Invalid Column Name

INPUT:
SQL> @tables.sql
OUTPUT:
SQL> spool tables.lst
SQL> set echo on
SQL> set feedback on
SQL> set pagesize 1000
SQL> select owner|| '.' || tablename
2 from sys.dba_tables
3 where owner = 'SYSTEM'
4 order by table_name
5 /
select owner|| '.' || tablename
*
ERROR at line 1:
ORA-00904: invalid column name
SQL> spool off
SQL>

ANALYSIS:
In line 1 the column tablename is incorrect. The correct column name is table_name. The underscore was omitted. To see the correct columns, use the DESCRIBE command. This error can also occur when trying to qualify a column in the SELECT statement by the wrong table name.