I am trying to reverse a string without using REVERSE function. I came across one example which is something like:
select listagg(letter) within group(order by lvl)
from
(SELECT LEVEL lvl, SUBSTR ('hello', LEVEL*-1, 1) letter
FROM dual
CONNECT BY LEVEL <= length('hello'));
Apart from this approach,is there any other better approach to do this?
If you're trying to avoid the undocumented reverse() function you could use the utl_raw.reverse() function instead, with appropriate conversion too and from RAW:
select utl_i18n.raw_to_char(
utl_raw.reverse(
utl_i18n.string_to_raw('Some string', 'AL32UTF8')), 'AL32UTF8')
from dual;
UTL_I18N.RAW_TO_CHAR(UTL_RAW.REVERSE(UTL_I18N.STRING_TO_RAW('SOMESTRING','AL32UT
--------------------------------------------------------------------------------
gnirts emoS
So that is taking an original value; doing utl_i18n.string_to_raw() on that; then passing that to utl_raw.reverse(); then passing the result of that back through utl_i18n.raw_to_char().
Not entirely sure how that will cope with multibyte characters, or what you'd want to happen to those anyway...
Or a variation from the discussion @RahulTripathi linked to, without the character set handling:
select utl_raw.cast_to_varchar2(utl_raw.reverse(utl_raw.cast_to_raw('Some string')))
from dual;
UTL_RAW.CAST_TO_VARCHAR2(UTL_RAW.REVERSE(UTL_RAW.CAST_TO_RAW('SOMESTRING')))
--------------------------------------------------------------------------------
gnirts emoS
But that thread also notes it only works for single-byte characters.
You could do it like this:
with strings as (select 'hello' str from dual union all
select 'fred' str from dual union all
select 'this is a sentance.' from dual)
select str,
replace(sys_connect_by_path(substr (str, level*-1, 1), '~|'), '~|') rev_str
from strings
where connect_by_isleaf = 1
connect by prior str = str --added because of running against several strings at once
and prior sys_guid() is not null --added because of running against several strings at once
and level <= length(str);
STR REV_STR
------------------- --------------------
fred derf
hello olleh
this is a sentance. .ecnatnes a si siht
N.B. I used a delimiter of ~| simply because that's something unlikely to be part of your string. You need to supply a non-null delimiter to the sys_connect_by_path, hence why I didn't just leave it blank!
SELECT LISTAGG(STR) WITHIN GROUP (ORDER BY RN DESC)
FROM
(
SELECT ROWNUM RN, SUBSTR('ORACLE',ROWNUM,1) STR FROM DUAL
CONNECT BY LEVEL <= LENGTH('ORACLE')
);
You can try using this function:
SQL> ed
Wrote file afiedt.buf
1 with t as (select 'Reverse' as txt from dual)
2 select replace(sys_connect_by_path(ch,'|'),'|') as reversed_string
3 from (
4 select length(txt)-rownum as rn, substr(txt,rownum,1) ch
5 from t
6 connect by rownum <= length(txt)
7 )
8 where connect_by_isleaf = 1
9 connect by rn = prior rn + 1
10* start with rn = 0
SQL> /
select listagg(rev)within group(order by rownum)
from
(select substr('Oracle',level*-1,1)rev from dual
connect by level<=length('Oracle'));
reverseonly works on VARCHAR (ascii) strings, not NVARCHAR (unicode) input. When I use it on nvarchar, I get what looks like Chinese characters, as output. I have toREVERSE(CAST(columnname AS VARCHAR(x)))if the input is nvarchar.