String operation in SQL to reverse a string - sql

Question

In DB2 9.7 I am looking for a way to reverse a string in a SQL query.
I am familiar with SQL Server where the query would be like
SELECT
REVERSE(LEFT_TO_REIGHT) AS RIGHT_TO_LEFT
FROM
TABLE1;
I couldn't find a similar function in DB2. is there a simple way to reverse a string?

Answer 1

Creating a REVERSE(..) function is unnecessary.
DB2 has something called RIGHT(string-expression, length):
The RIGHT function returns the rightmost string of string-expression
of length length, expressed in the specified string unit. If
string-expression is a character string, the result is a character
string. If string-expression is a graphic string, the result is a
graphic string
So if you're interested in the last 8 characters, you can pretty trivially do this via:
SELECT RIGHT(left_to_right, 8) AS right_to_left
FROM Table1
(I'm actually still concerned about the fact that you're splitting off 8 characters consistently, as it implies you have a multi-part key of some sort).

Answer 2

Try something like:
SELECT STRIP(CAST( TRANSLATE('87654321',LEFT_TO_REIGHT, '12345678') AS VARCHAR(8) ))
FROM TABLE1;

Answer 3

Due to the original question this is the first webpage that comes up when one searches for 'How to reverse a string in DB2'.
Here is an answer that doesn't require implementing it in C and shouldn't brake on non-pure-Engilsh strings regardless of their length.
Be warned though, the efficiency is 'meh' at best.
CREATE FUNCTION REVERSE_STRING(STR VARCHAR(100))
RETURNS VARCHAR(100)
LANGUAGE SQL
SPECIFIC REVERSE_STRING
DETERMINISTIC
REVERSE: BEGIN
DECLARE REVERSED_STRING VARCHAR(100);
DECLARE REVERSED_CHARACTERS_INDEX INTEGER;
SET REVERSED_STRING='';
SET REVERSED_CHARACTERS_INDEX=0;
WHILE (REVERSED_CHARACTERS_INDEX < CHARACTER_LENGTH(STR, CODEUNITS16))
DO
SET REVERSED_CHARACTERS_INDEX = REVERSED_CHARACTERS_INDEX + 1;
SET REVERSED_STRING = CONCAT(
REVERSED_STRING,
LEFT(RIGHT(STR, REVERSED_CHARACTERS_INDEX, CODEUNITS16), 1, CODEUNITS16));
END WHILE;
RETURN REVERSED_STRING;
END REVERSE#
The idea is to get a substring which starts from the n-th character from the right till the end of the string, then take the first element of this substring from the left and append it to a reversed string. This operation is conducted n times where n is the length of a string to be reversed.
You can use it like any other function.
SELECT FIRSTNME AS FIRSTNAME, REVERSE_STRING(FIRSTNME) AS REVERSED_FIRSTNAME
FROM SAMPLE.EMPLOYEE#
Example output

Answer 4

Answering the original question of reversing a string there's user defined functions published on the IBM site that will do it that you can find here. There's apparently no built in ability in DB2
https://www.ibm.com/developerworks/community/blogs/SQLTips4DB2LUW/entry/reverse?lang=en
Tortured SQL version:
CREATE OR REPLACE FUNCTION REVERSE(INSTR VARCHAR(4000))
RETURNS VARCHAR(4000) SPECIFIC REVERSE
DETERMINISTIC NO EXTERNAL ACTION CONTAINS SQL
RETURN WITH rec(pos, res) AS (VALUES (1, CAST('' AS VARCHAR(4000)))
UNION ALL
SELECT pos + 1, SUBSTR(INSTR, pos , 1) || res
FROM rec
WHERE pos <= LENGTH(INSTR)
AND pos < 5000)
SELECT res FROM rec WHERE pos > LENGTH(INSTR);
But then you have to do this as well, yuck:
CREATE BUFFERPOOL bp32 PAGESIZE 32K;
CREATE SYSTEM TEMPORARY TABLESPACE tsp32 PAGESIZE 32K BUFFERPOOL bp32;
A saner C implementation
#include <sqludf.h>
#ifdef __cplusplus
extern "C"
#endif
void SQL_API_FN ReverseSBCP(SQLUDF_VARCHAR *inVarchar,
SQLUDF_VARCHAR *outVarchar,
SQLUDF_SMALLINT *inVarcharNullInd,
SQLUDF_SMALLINT *outVarcharNullInd,
SQLUDF_TRAIL_ARGS)
{
int inLen, inPos, outPos;
if (*inVarcharNullInd == -1)
{
*outVarcharNullInd = -1;
}
else
{
inLen = strlen(inVarchar);
for (inPos = 0, outPos = inLen -1; inPos < inLen; inPos++, outPos--)
{
outVarchar[outPos] = inVarchar[inPos];
}
outVarchar[inLen] = '\0';
*outVarcharNullInd = 0;
}
return;
}