A procedure to Reverse a String in PL/SQL - sql

Question

I just started learning PL/SQL and I'm not sure how to create a procedure. The logic seems about right but I think there's some syntactical mistake in the first line. Here's my code:-
CREATE OR REPLACE PROCEDURE ReverseOf(input IN varchar2(50)) IS
DECLARE
reverse varchar2(50);
BEGIN
FOR i in reverse 1..length(input) LOOP
reverse := reverse||''||substr(input, i, 1);
END LOOP;
dbms_output.put_line(reverse);
END;
/

Answer 1

Two things - you shouldn't specify the datatype size in procedure's/function's parameter list and you do not need the DECLARE keyword. Try this:
CREATE OR REPLACE PROCEDURE ReverseOf(input IN varchar2) IS
rev varchar2(50):='';
BEGIN
FOR i in reverse 1..length(input) LOOP
rev := rev||substr(input, i, 1);
END LOOP;
dbms_output.put_line(rev);
END;

Answer 2

Try it without PL/SQL!
WITH
params AS
(SELECT 'supercalifragilisticexpialidocious' phrase FROM dual),
WordReverse (inpt, outpt) AS
(SELECT phrase inpt, CAST(NULL AS varchar2(4000)) outpt FROM params
UNION ALL
SELECT substr(inpt,2,LENGTH(inpt)-1), substr(inpt,1,1) || outpt
FROM wordReverse
WHERE LENGTH(inpt) > 0
)
SELECT phrase,outpt AS reversed FROM wordReverse, params
WHERE LENGTH(outpt) = LENGTH(phrase) ;
PHRASE REVERSED
---------------------------------- -----------------------------------
supercalifragilisticexpialidocious suoicodilaipxecitsiligarfilacrepus
Citation: http://rdbms-insight.com/wp/?p=94

Answer 3

Another solution reverse string minimizing loop count
DECLARE
v_str VARCHAR2(100) DEFAULT 'MYSTRING';
v_len NUMBER;
v_left VARCHAR2(100);
v_right VARCHAR2(100);
BEGIN
v_len := LENGTH(v_str)/2;
FOR rec IN 1..v_len
LOOP
v_left := substr(v_str,rec,1) || v_left;
IF rec * 2 <= LENGTH(v_str) THEN
v_right := v_right || substr(v_str,-rec,1);
END IF;
END LOOP;
v_str := v_right || v_left;
dbms_output.put_line(v_str);
END;

Answer 4

set serveroutput on
declare
str1 varchar2(30);
len number(3);
str2 varchar2(30);
i number(3);
begin
str1:='&str1';
len:=length(str1);
for i in reverse 1..len
loop
str2:=str2 || substr(str1,i,1);
end loop;
dbms_output.put_line('Reverse string is: '||str2);
end;
/

Answer 5

create or replace procedure ap_reverse_number(input_no VARCHAR2) as
output_no VARCHAR2(100);
begin
for i in 1 .. length(input_no) loop
output_no := output_no || '' ||
substr(input_no, (length(input_no) - i + 1), 1);
end loop;
dbms_output.put_line('Input no. is :' || input_no);
dbms_output.put_line('Output no. is:' || output_no);
end;
This should do the job correctly.

Answer 6

Try this one line statement to reverse the string in sql
with a as (select 'brahma' k from dual)
select listagg(substr(k,length(k)-level+1,1),'') within group (order by 1) b from a connect by level<length(k)+1

Answer 7

Try this one line query to reverse a string or a number.
select reverse('HelloWorld') from dual;

Answer 8

declare
name varchar2(20):='&name';
rname varchar2(20);
begin
for i in reverse 1..length(name)
loop
rname:=rname||substr(name,i,1);
end loop;
display(rname);
end;