SQL> select cust_code from ar_cust where rownum<=1;

CUST_CODE
----------
03004009

SQL> select cust_code abcdefghijklmnopqrstuvwxyz1234 from ar_cust where rownum<=1;

ABCDEFGHIJ
----------
03004009

SQL> select cust_code abcdefghijklmnopqrstuvwxyz12345 from ar_cust where rownum<=1;
select cust_code abcdefghijklmnopqrstuvwxyz12345 from ar_cust where rownum<=1
                 *
ERROR at line 1:
ORA-00972: identifier is too long


SQL> select cust_code as abcdefghijklmnopqrstuvwxyz12345 from ar_cust where rownum<=1;
select cust_code as abcdefghijklmnopqrstuvwxyz12345 from ar_cust where rownum<=1
                    *
ERROR at line 1:
ORA-00972: identifier is too long

column col1 heading 'abcdefghijklmnopqrstuvwxyz12345' 

select rpad(ename,60)  as col1 from emp;