While loop PL/SQL read a string backwards [duplicate]

Question

i need help with this question, Using PL/SQL how can I read a string backwards using the while loop?

I know that with the for loop there is a method called reverse but I don't know how I can do it with the while loop. If you can help me I appreciate it

Answer 1

Here's one option:

SQL> set serveroutput on
SQL>
SQL> declare
  2    l_str   varchar2(20) := 'Littlefoot';
  3    i       number;
  4    retval  varchar2(20);
  5  begin
  6    i := length(l_str);
  7    while i <> 0 loop
  8      retval := retval || substr(l_str, i, 1);
  9      i := i - 1;
 10    end loop;
 11    dbms_output.put_line(retval);
 12  end;
 13  /
toofelttiL

PL/SQL procedure successfully completed.

SQL>

---

If it doesn't have to be PL/SQL, hierarchical query along with listagg might be another way to do it:

SQL> var l_str varchar2(20)
SQL> exec :l_str := 'Littlefoot';

PL/SQL procedure successfully completed.

SQL> select listagg(substr(:l_str, length(:l_str) - level + 1, 1), '') within group (order by level) result
  2  from dual
  3  connect by level <= length(:l_str);

RESULT
--------------------------------------------------------------------------------
toofelttiL

SQL>