hi,
just go thru the example below.

y the function REVERSE doesn't work in a PL/SQL block?

-----------------------------------------------------------------------
SQL> select reverse('jegan') from dual;

REVER
-----
nagej

-----------------------------------------------------------------------
declare
a varchar2(100);
begin
select reverse('jegan') into a from dual;
dbms_output.put_line(a);
end;
SQL> /
declare
*
ERROR at line 1:
ORA-06550: line 4, column 8:
PLS-00201: identifier 'REVERSE' must be declared
ORA-06550: line 4, column 1:
PL/SQL: SQL Statement ignored