Missing Expression

INPUT:
SQL> @tables.sql

OUTPUT:
SQL> spool tables.lst
SQL> set echo on
SQL> set feedback on
SQL> set pagesize 1000
SQL> select owner|| '.' || table,
2 from sys.dba_tables
3 where owner = 'SYSTEM'
4 order by table_name
5 /
from sys.dba_tables
*
ERROR at line 2:
ORA-00936: missing expression
SQL> spool off
SQL>

ANALYSIS:
Notice the comma after table on the first line; therefore, the query processor is
looking for another column in the SELECT clause. At this point, the processor is not
expecting the FROM clause.
Not Enough Arguments for Function
INPUT:
SQL> @tblspc.sqlOUTPUT:
SQL> spool tblspc.lst
SQL> set echo on
SQL> set feedback on
SQL> set pagesize 1000
SQL> select substr(tablespace_name,1,15) a,
2 decode(substr(file_name,1,45)) c, bytes
3 from sys.dba_data_files
4 order by tablespace_name;
decode(substr(file_name,1,45)) c, bytes
*
ERROR at line 2:
ORA-00938: not enough arguments for function
SQL> spool off
SQL>
ANALYSIS:
There are not enough arguments for the DECODE function. Check your implementation for the proper syntax.