MySQL REPLACE() – Replace All Instances of a Substring with another String

The MySQL REPLACE() function enables you to replace all occurrences of a substring with another string. It allows you to do things like, replace all occurrences of one word with another word, etc.

This article demonstrates its usage.

Syntax

Here’s how the syntax goes:

REPLACE(str,from_str,to_str)

Where str is the string that contains the substring/s. from_str is the substring you want to replace with another string. And to_str is the new string that will replace the old string.

Example

Here’s a basic example:

SELECT REPLACE('Cats and dogs and cats and rabbits', 'and', 'or') AS Result;

Result:

+---------------------------------+
| Result                          |
+---------------------------------+
| Cats or dogs or cats or rabbits |
+---------------------------------+

In this case, we simply swap the word and with the word or. Because there were three occurrences of that word, all three were replaced.

Case-Sensitve

It’s important to remember that the REPLACE() function is case-sensitive.

Example:

SELECT REPLACE('Cats and dogs and cats and rabbits', 'cat', 'flea') AS Result;

Result:

+-------------------------------------+
| Result                              |
+-------------------------------------+
| Cats and dogs and fleas and rabbits |
+-------------------------------------+

In this case, only one instance of cat was replaced, because only one instance had the right case. The first instance had an uppercase C so it didn’t match.

Remove a Substring

You can also remove a substring altogether, simply by replacing the substring with the empty string (''):

SELECT REPLACE('http://www.database.guide', 'www.', '') AS Result;

Result:

+-----------------------+
| Result                |
+-----------------------+
| http://database.guide |
+-----------------------+

A Safeguard

Another (perhaps safer) way of doing this is to include some of the surrounding text, then remove the unnecessary part:

SELECT REPLACE('http://www.database.guide', 'http://www.', 'http://') AS Result;

Result:

+-----------------------+
| Result                |
+-----------------------+
| http://database.guide |
+-----------------------+

This guards against inadvertently removing a substring that shouldn’t be removed. For example, if we have a URL like  http://bestwww.com, which would inadvertently turn into http://bestcom without the safeguard.

The same safeguard can be applied in cases where you’re replacing text (not just removing it). For example, this:

SELECT REPLACE('Land of cats and dogs and sand', ' and ', ' or ') AS Result;

Result:

+------------------------------+
| Result                       |
+------------------------------+
| Land of cats or dogs or sand |
+------------------------------+

In this case I added a space before and after the substring and its replacement text.

If I hadn’t done this, I would’ve ended up with this:

SELECT REPLACE('Land of cats and dogs and sand', 'and', 'or') AS Result;

Result:

+----------------------------+
| Result                     |
+----------------------------+
| Lor of cats or dogs or sor |
+----------------------------+

How to do a regular expression replace in MySQL?

I have a table with ~500k rows; varchar(255) UTF8 column filename contains a file name;

I'm trying to strip out various strange characters out of the filename - thought I'd use a character class: [^a-zA-Z0-9()_ .\-]

Now, is there a function in MySQL that lets you replace through a regular expression? I'm looking for a similar functionality to REPLACE() function - simplified example follows:

SELECT REPLACE('stackowerflow', 'ower', 'over');

Output: ""

/* does something like this exist? */
SELECT X_REG_REPLACE('','/[A-Zf]/','-'); 

Output: "-tackover-low"

I know about REGEXP/RLIKE, but those only check if there is a match, not what the match is.

(I could do a "SELECT pkey_id,filename FROM foo WHERE filename RLIKE '[^a-zA-Z0-9()_ .\-]'" from a PHP script, do a preg_replace and then "UPDATE foo ... WHERE pkey_id=...", but that looks like a last-resort slow & ugly hack)

 Answers

MySQL 8.0+ you could use natively REGEXP_REPLACE.

12.5.2 Regular Expressions:

REGEXP_REPLACE(expr, pat, repl[, pos[, occurrence[, match_type]]])

Replaces occurrences in the string expr that match the regular expression specified by the pattern pat with the replacement string repl, and returns the resulting string. If expr, pat, or repl is NULL, the return value is NULL.

and Regular expression support:

Previously, MySQL used the Henry Spencer regular expression library to support regular expression operators (REGEXP, RLIKE).

Regular expression support has been reimplemented using International Components for Unicode (ICU), which provides full Unicode support and is multibyte safe. The REGEXP_LIKE() function performs regular expression matching in the manner of the REGEXP and RLIKE operators, which now are synonyms for that function. In addition, the REGEXP_INSTR(), REGEXP_REPLACE(), and REGEXP_SUBSTR() functions are available to find match positions and perform substring substitution and extraction, respectively.

---

Use MariaDB instead. It has a function

REGEXP_REPLACE(col, regexp, replace)

See MariaDB docs and PCRE Regular expression enhancements

Note that you can use regexp grouping as well (I found that very useful):

SELECT REGEXP_REPLACE("", "(stack)(over)(flow)", '\\2 - \\1 - \\3')

returns

over - stack - flow

---

I recently wrote a MySQL function to replace strings using regular expressions. You could find my post at the following location:

https://thiscode4u.blogspot.com/2018/11/regex-replace-for-mysql.html

Here is the function code:

DELIMITER $$

CREATE FUNCTION  `regex_replace`(pattern VARCHAR(1000),replacement VARCHAR(1000),original VARCHAR(1000))
RETURNS VARCHAR(1000)
DETERMINISTIC
BEGIN 
 DECLARE temp VARCHAR(1000); 
 DECLARE ch VARCHAR(1); 
 DECLARE i INT;
 SET i = 1;
 SET temp = '';
 IF original REGEXP pattern THEN 
  loop_label: LOOP 
   IF i>CHAR_LENGTH(original) THEN
    LEAVE loop_label;  
   END IF;
   SET ch = SUBSTRING(original,i,1);
   IF NOT ch REGEXP pattern THEN
    SET temp = CONCAT(temp,ch);
   ELSE
    SET temp = CONCAT(temp,replacement);
   END IF;
   SET i=i+1;
  END LOOP;
 ELSE
  SET temp = original;
 END IF;
 RETURN temp;
END$$

DELIMITER ;

Example execution:

mysql> select regex_replace('[^a-zA-Z0-9\-]','','2my test3_text-to. check \\ my- sql (regular) ,expressions ._,');

---

I'm happy to report that since this question was asked, now there is a satisfactory answer! Take a look at this terrific package:

https://github.com/mysqludf/lib_mysqludf_preg

Sample SQL:

SELECT PREG_REPLACE('/(.*?)(fox)/' , 'dog' , 'the quick brown fox' ) AS demo;

---

UPDATE: Have now made this into a blog post: https://thiscode4u.blogspot.com/2018/11/a-mysql-regular-expression-replace.html

---

Through all necessary substrings rather than just testing single characters:

-- ------------------------------------------------------------------------------------
-- USAGE
-- ------------------------------------------------------------------------------------
-- SELECT reg_replace(<subject>,
--                    <pattern>,
--                    <replacement>,
--                    <greedy>,
--                    <minMatchLen>,
--                    <maxMatchLen>);
-- where:
-- <subject> is the string to look in for doing the replacements
-- <pattern> is the regular expression to match against
-- <replacement> is the replacement string
-- <greedy> is TRUE for greedy matching or FALSE for non-greedy matching
-- <minMatchLen> specifies the minimum match length
-- <maxMatchLen> specifies the maximum match length
-- (minMatchLen and maxMatchLen are used to improve efficiency but are
--  optional and can be set to 0 or NULL if not known/required)
-- Example:
-- SELECT reg_replace(txt, '^[Tt][^ ]* ', 'a', TRUE, 2, 0) FROM tbl;
DROP FUNCTION IF EXISTS reg_replace;
DELIMITER //
CREATE FUNCTION reg_replace(subject VARCHAR(21845), pattern VARCHAR(21845),
  replacement VARCHAR(21845), greedy BOOLEAN, minMatchLen INT, maxMatchLen INT)
RETURNS VARCHAR(21845) DETERMINISTIC BEGIN 
  DECLARE result, subStr, usePattern VARCHAR(21845); 
  DECLARE startPos, prevStartPos, startInc, len, lenInc INT;
  IF subject REGEXP pattern THEN
    SET result = '';
    -- Sanitize input parameter values
    SET minMatchLen = IF(minMatchLen < 1, 1, minMatchLen);
    SET maxMatchLen = IF(maxMatchLen < 1 OR maxMatchLen > CHAR_LENGTH(subject),
                         CHAR_LENGTH(subject), maxMatchLen);
    -- Set the pattern to use to match an entire string rather than part of a string
    SET usePattern = IF (LEFT(pattern, 1) = '^', pattern, CONCAT('^', pattern));
    SET usePattern = IF (RIGHT(pattern, 1) = '$', usePattern, CONCAT(usePattern, '$'));
    -- Set start position to 1 if pattern starts with ^ or doesn't end with $.
    IF LEFT(pattern, 1) = '^' OR RIGHT(pattern, 1) <> '$' THEN
      SET startPos = 1, startInc = 1;
    -- Otherwise (i.e. pattern ends with $ but doesn't start with ^): Set start pos
    -- to the min or max match length from the end (depending on "greedy" flag).
    ELSEIF greedy THEN
      SET startPos = CHAR_LENGTH(subject) - maxMatchLen + 1, startInc = 1;
    ELSE
      SET startPos = CHAR_LENGTH(subject) - minMatchLen + 1, startInc = -1;
    END IF;
    WHILE startPos >= 1 AND startPos <= CHAR_LENGTH(subject)
      AND startPos + minMatchLen - 1 <= CHAR_LENGTH(subject)
      AND !(LEFT(pattern, 1) = '^' AND startPos <> 1)
      AND !(RIGHT(pattern, 1) = '$'
            AND startPos + maxMatchLen - 1 < CHAR_LENGTH(subject)) DO
      -- Set start length to maximum if matching greedily or pattern ends with $.
      -- Otherwise set starting length to the minimum match length.
      IF greedy OR RIGHT(pattern, 1) = '$' THEN
        SET len = LEAST(CHAR_LENGTH(subject) - startPos + 1, maxMatchLen), lenInc = -1;
      ELSE
        SET len = minMatchLen, lenInc = 1;
      END IF;
      SET prevStartPos = startPos;
      lenLoop: WHILE len >= 1 AND len <= maxMatchLen
                 AND startPos + len - 1 <= CHAR_LENGTH(subject)
                 AND !(RIGHT(pattern, 1) = '$' 
                       AND startPos + len - 1 <> CHAR_LENGTH(subject)) DO
        SET subStr = SUBSTRING(subject, startPos, len);
        IF subStr REGEXP usePattern THEN
          SET result = IF(startInc = 1,
                          CONCAT(result, replacement), CONCAT(replacement, result));
          SET startPos = startPos + startInc * len;
          LEAVE lenLoop;
        END IF;
        SET len = len + lenInc;
      END WHILE;
      IF (startPos = prevStartPos) THEN
        SET result = IF(startInc = 1, CONCAT(result, SUBSTRING(subject, startPos, 1)),
                        CONCAT(SUBSTRING(subject, startPos, 1), result));
        SET startPos = startPos + startInc;
      END IF;
    END WHILE;
    IF startInc = 1 AND startPos <= CHAR_LENGTH(subject) THEN
      SET result = CONCAT(result, RIGHT(subject, CHAR_LENGTH(subject) + 1 - startPos));
    ELSEIF startInc = -1 AND startPos >= 1 THEN
      SET result = CONCAT(LEFT(subject, startPos), result);
    END IF;
  ELSE
    SET result = subject;
  END IF;
  RETURN result;
END//
DELIMITER ;

Demo

Rextester Demo

Limitations

1. This method is of course going to take a while when the subject string is large. Update: Have now added minimum and maximum match length parameters for improved efficiency when these are known (zero = unknown/unlimited).
2. It won't allow substitution of backreferences (e.g. \1, \2 etc.) to replace capturing groups. If this functionality is needed, please see this answer which attempts to provide a workaround by updating the function to allow a secondary find and replace within each found match (at the expense of increased complexity).
3. If ^and/or $ is used in the pattern, they must be at the very start and very end respectively - e.g. patterns such as (^start|end$) are not supported.
4. There is a "greedy" flag to specify whether the overall matching should be greedy or non-greedy. Combining greedy and lazy matching within a single regular expression (e.g. a.*?b.*) is not supported.

A MySQL regular expression replace function

If you're using MySQL, you may have come across its REGEXP (a.k.a. RLIKE) operator, which can be used as a more powerful alternative to the LIKE operator. For example:

SELECT * FROM address WHERE postcode REGEXP '^[A-Z]{1,2}[0-9]{1,2} ?[0-9][A-Z]{2}$';

But despite having a competent regular expression engine, MySQL doesn't provide a built-in regular expression replace function. **UPDATE**: A useful set of regex functions including REGEXP_REPLACE have now been provided in MySQL 8.0. This renders reading on unnecessary unless you're constrained to using an earlier version. It's worth noting that MariaDB does provide such a function - but that won't help if you're working on an established project that's tied to MySQL (or have other reasons for wanting to stay with it).

There have been some valiant attempts to plug the gap via User-Defined Function libraries that can be compiled from C source code and incorporated into a MySQL server instance: mysql-udf-regexp and lib_mysqludf_preg. But these do require the MySQL source code to be present and appropriate permissions to compile and build the files on the server.

Surely there could be a lighter-weight alternative...? Given that REGEXP can test whether a substring matches a regular expression, couldn't it be used to look inside a find string, get the bits that match and then replace them? Well that turns out to be a bit harder than it might sound as there are some additional complexities to consider such as start and end anchors, greedy/non-greedy matching etc. But I've written a function that will do the basic job, as shown in this Rextester online demo. Here's the code:

-- ------------------------------------------------------------------------------------
-- USAGE
-- ------------------------------------------------------------------------------------
-- SELECT reg_replace(<subject>,
--                    <pattern>,
--                    <replacement>,
--                    <greedy>,
--                    <minMatchLen>,
--                    <maxMatchLen>);
-- where:
-- <subject> is the string to look in for doing the replacements
-- <pattern> is the regular expression to match against
-- <replacement> is the replacement string
-- <greedy> is TRUE for greedy matching or FALSE for non-greedy matching
-- <minMatchLen> specifies the minimum match length
-- <maxMatchLen> specifies the maximum match length
-- (minMatchLen and maxMatchLen are used to improve efficiency but are
--  optional and can be set to 0 or NULL if not known/required)
-- Example:
-- SELECT reg_replace(txt, '^[Tt][^ ]* ', 'a', TRUE, 2, 0) FROM tbl;
DROP FUNCTION IF EXISTS reg_replace;
DELIMITER //
CREATE FUNCTION reg_replace(subject VARCHAR(21845), pattern VARCHAR(21845),
  replacement VARCHAR(21845), greedy BOOLEAN, minMatchLen INT, maxMatchLen INT)
RETURNS VARCHAR(21845) DETERMINISTIC BEGIN 
  DECLARE result, subStr, usePattern VARCHAR(21845); 
  DECLARE startPos, prevStartPos, startInc, len, lenInc INT;
  IF subject REGEXP pattern THEN
    SET result = '';
    -- Sanitize input parameter values
    SET minMatchLen = IF(minMatchLen < 1, 1, minMatchLen);
    SET maxMatchLen = IF(maxMatchLen < 1 OR maxMatchLen > CHAR_LENGTH(subject),
                         CHAR_LENGTH(subject), maxMatchLen);
    -- Set the pattern to use to match an entire string rather than part of a string
    SET usePattern = IF (LEFT(pattern, 1) = '^', pattern, CONCAT('^', pattern));
    SET usePattern = IF (RIGHT(pattern, 1) = '$', usePattern, CONCAT(usePattern, '$'));
    -- Set start position to 1 if pattern starts with ^ or doesn't end with $.
    IF LEFT(pattern, 1) = '^' OR RIGHT(pattern, 1) <> '$' THEN
      SET startPos = 1, startInc = 1;
    -- Otherwise (i.e. pattern ends with $ but doesn't start with ^): Set start pos
    -- to the min or max match length from the end (depending on "greedy" flag).
    ELSEIF greedy THEN
      SET startPos = CHAR_LENGTH(subject) - maxMatchLen + 1, startInc = 1;
    ELSE
      SET startPos = CHAR_LENGTH(subject) - minMatchLen + 1, startInc = -1;
    END IF;
    WHILE startPos >= 1 AND startPos <= CHAR_LENGTH(subject)
      AND startPos + minMatchLen - 1 <= CHAR_LENGTH(subject)
      AND !(LEFT(pattern, 1) = '^' AND startPos <> 1)
      AND !(RIGHT(pattern, 1) = '$'
            AND startPos + maxMatchLen - 1 < CHAR_LENGTH(subject)) DO
      -- Set start length to maximum if matching greedily or pattern ends with $.
      -- Otherwise set starting length to the minimum match length.
      IF greedy OR RIGHT(pattern, 1) = '$' THEN
        SET len = LEAST(CHAR_LENGTH(subject) - startPos + 1, maxMatchLen), lenInc = -1;
      ELSE
        SET len = minMatchLen, lenInc = 1;
      END IF;
      SET prevStartPos = startPos;
      lenLoop: WHILE len >= 1 AND len <= maxMatchLen
                 AND startPos + len - 1 <= CHAR_LENGTH(subject)
                 AND !(RIGHT(pattern, 1) = '$' 
                       AND startPos + len - 1 <> CHAR_LENGTH(subject)) DO
        SET subStr = SUBSTRING(subject, startPos, len);
        IF subStr REGEXP usePattern THEN
          SET result = IF(startInc = 1,
                          CONCAT(result, replacement), CONCAT(replacement, result));
          SET startPos = startPos + startInc * len;
          LEAVE lenLoop;
        END IF;
        SET len = len + lenInc;
      END WHILE;
      IF (startPos = prevStartPos) THEN
        SET result = IF(startInc = 1, CONCAT(result, SUBSTRING(subject, startPos, 1)),
                        CONCAT(SUBSTRING(subject, startPos, 1), result));
        SET startPos = startPos + startInc;
      END IF;
    END WHILE;
    IF startInc = 1 AND startPos <= CHAR_LENGTH(subject) THEN
      SET result = CONCAT(result, RIGHT(subject, CHAR_LENGTH(subject) + 1 - startPos));
    ELSEIF startInc = -1 AND startPos >= 1 THEN
      SET result = CONCAT(LEFT(subject, startPos), result);
    END IF;
  ELSE
    SET result = subject;
  END IF;
  RETURN result;
END//
DELIMITER ;

Limitations

1. The CREATE ROUTINE privilege is required for creating the function.
2. It only supports VARCHAR(21845) rather than the larger TEXT data type.
3. This method is of course going to take a while when the subject string is large.
4. If ^ and/or $ anchors are used in the pattern, they must be at the very start and very end respectively - e.g. patterns such as (^start|end$) aren't supported.
5. There is a "greedy" flag to specify whether the overall matching should be greedy or non-greedy. Combining greedy and lazy matching within a single regular expression (e.g. a.*?b.*) isn't supported.
6. It won't allow substitution of backreferences (e.g. \1, \2 etc.) to replace capturing groups. If this functionality is needed, please see the more advanced version below, which attempts to provide a workaround by updating the function to allow a secondary find and replace within each found match (at the expense of increased complexity).

More advanced version
The following more advanced version goes some way towards addressing limitation (6) above by allowing a further "sub-pattern" to further restrict what is actually replaced within each match, as shown in this Rextester online demo. It actually consists of a function and an internally used stored procedure since a recursive call is needed and recursion is only supported by stored procedures, not functions in MySQL. Here's the code:

-- ------------------------------------------------------------------------------------
-- USAGE
-- ------------------------------------------------------------------------------------
-- SELECT reg_replace(<subject>,
--                    <pattern>,
--                    <subpattern>,
--                    <replacement>,
--                    <greedy>,
--                    <minMatchLen>,
--                    <maxMatchLen>,
--                    <minSubMatchLen>,
--                    <maxSubMatchLen>);
-- where:
-- <subject> is the string to look in for doing the replacements
-- <pattern> is the regular expression to match against
-- <subpattern> is a regular expression to match against within each
--              portion of text that matches <pattern>
-- <replacement> is the replacement string
-- <greedy> is TRUE for greedy matching or FALSE for non-greedy matching
-- <minMatchLen> specifies the minimum match length
-- <maxMatchLen> specifies the maximum match length
-- <minSubMatchLen> specifies the minimum match length
-- <maxSubMatchLen> specifies the maximum match length
-- (minMatchLen, maxMatchLen, minSubMatchLen and maxSubMatchLen are used to improve
--  efficiency but are optional and can be set to 0 or NULL if not known/required)
-- Example:
-- SELECT reg_replace(txt, '[A-Z0-9]{3}', '[0-9]', '_', TRUE, 3, 3, 1, 1) FROM tbl;
DROP FUNCTION IF EXISTS reg_replace;
DELIMITER //
CREATE FUNCTION reg_replace(subject VARCHAR(21845), pattern VARCHAR(21845),
  subpattern VARCHAR(21845), replacement VARCHAR(21845), greedy BOOLEAN,
  minMatchLen INT, maxMatchLen INT, minSubMatchLen INT, maxSubMatchLen INT)
RETURNS VARCHAR(21845) DETERMINISTIC BEGIN
  DECLARE result VARCHAR(21845);
  CALL reg_replace_worker(
    subject, pattern, subpattern, replacement, greedy, minMatchLen, maxMatchLen,
    minSubMatchLen, maxSubMatchLen, result);
  RETURN result;
END;//
DELIMITER ;

DROP PROCEDURE IF EXISTS reg_replace_worker;
DELIMITER //
CREATE PROCEDURE reg_replace_worker(subject VARCHAR(21845), pattern VARCHAR(21845),
  subpattern VARCHAR(21845), replacement VARCHAR(21845), greedy BOOLEAN,
  minMatchLen INT, maxMatchLen INT, minSubMatchLen INT, maxSubMatchLen INT,
  OUT result VARCHAR(21845))
BEGIN
  DECLARE subStr, usePattern, useRepl VARCHAR(21845);
  DECLARE startPos, prevStartPos, startInc, len, lenInc INT;
  SET @@SESSION.max_sp_recursion_depth = 2;
  IF subject REGEXP pattern THEN
    SET result = '';
    -- Sanitize input parameter values
    SET minMatchLen = IF(minMatchLen < 1, 1, minMatchLen);
    SET maxMatchLen = IF(maxMatchLen < 1 OR maxMatchLen > CHAR_LENGTH(subject),
                         CHAR_LENGTH(subject), maxMatchLen);
    -- Set the pattern to use to match an entire string rather than part of a string
    SET usePattern = IF (LEFT(pattern, 1) = '^', pattern, CONCAT('^', pattern));
    SET usePattern = IF (RIGHT(pattern, 1) = '$', usePattern, CONCAT(usePattern, '$'));
    -- Set start position to 1 if pattern starts with ^ or doesn't end with $.
    IF LEFT(pattern, 1) = '^' OR RIGHT(pattern, 1) <> '$' THEN
      SET startPos = 1, startInc = 1;
    -- Otherwise (i.e. pattern ends with $ but doesn't start with ^): Set start pos
    -- to the min or max match length from the end (depending on "greedy" flag).
    ELSEIF greedy THEN
      SET startPos = CHAR_LENGTH(subject) - maxMatchLen + 1, startInc = 1;
    ELSE
      SET startPos = CHAR_LENGTH(subject) - minMatchLen + 1, startInc = -1;
    END IF;
    WHILE startPos >= 1 AND startPos <= CHAR_LENGTH(subject)
      AND startPos + minMatchLen - 1 <= CHAR_LENGTH(subject)
      AND !(LEFT(pattern, 1) = '^' AND startPos <> 1)
      AND !(RIGHT(pattern, 1) = '$'
            AND startPos + maxMatchLen - 1 < CHAR_LENGTH(subject)) DO
      -- Set start length to maximum if matching greedily or pattern ends with $.
      -- Otherwise set starting length to the minimum match length.
      IF greedy OR RIGHT(pattern, 1) = '$' THEN
        SET len = LEAST(CHAR_LENGTH(subject) - startPos + 1, maxMatchLen), lenInc = -1;
      ELSE
        SET len = minMatchLen, lenInc = 1;
      END IF;
      SET prevStartPos = startPos;
      lenLoop: WHILE len >= 1 AND len <= maxMatchLen
                 AND startPos + len - 1 <= CHAR_LENGTH(subject)
                 AND !(RIGHT(pattern, 1) = '$' 
                       AND startPos + len - 1 <> CHAR_LENGTH(subject)) DO
        SET subStr = SUBSTRING(subject, startPos, len);
        IF subStr REGEXP usePattern THEN
          IF subpattern IS NULL THEN
            SET useRepl = replacement;
          ELSE
            CALL reg_replace_worker(subStr, subpattern, NULL, replacement, greedy, 
                          minSubMatchLen, maxSubMatchLen, NULL, NULL, useRepl);
          END IF;
          SET result = IF(startInc = 1,
                          CONCAT(result, useRepl), CONCAT(useRepl, result));
          SET startPos = startPos + startInc * len;
          LEAVE lenLoop;
        END IF;
        SET len = len + lenInc;
      END WHILE;
      IF (startPos = prevStartPos) THEN
        SET result = IF(startInc = 1, CONCAT(result, SUBSTRING(subject, startPos, 1)),
                        CONCAT(SUBSTRING(subject, startPos, 1), result));
        SET startPos = startPos + startInc;
      END IF;
    END WHILE;
    IF startInc = 1 AND startPos <= CHAR_LENGTH(subject) THEN
      SET result = CONCAT(result, RIGHT(subject, CHAR_LENGTH(subject) + 1 - startPos));
    ELSEIF startInc = -1 AND startPos >= 1 THEN
      SET result = CONCAT(LEFT(subject, startPos), result);
    END IF;
  ELSE
    SET result = subject;
  END IF;
END;//
DELIMITER ;