How to remove all non-alpha numeric characters from a string in MySQL

Question

I m working on a routine that compares strings  but for better efficiency I need to remove all characters that are not letters or numbers   I m using multiple REPLACE functions now  but maybe there is a faster and nicer solution

User · Answer

From a performance point of view   and on the assumption that you read more than you write   I think the best way would be to pre calculate and store a stripped version of the column   This way you do the transform less   You can then put an index on the new column and get the database to do the work for you

User · Answer

SELECT teststring REGEXP     alnum        SELECT   FROM testtable WHERE test REGEXP     alnum          See  http   dev mysql com doc refman 5 1 en regexp html Scroll down to the section that says    character class    If you want to manipulate strings the fastest way will be to use a str udf  see  https   github com hholzgra mysql-udf-regexp

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if you are using php then       try   con   new PDO   mysql host localhost dbname dbasename   root         catch PDOException  e   echo  error   e-getMessage           select    con- gt prepare  SELECT   FROM table     select- gt setFetchMode PDO  FETCH ASSOC    select- gt execute     while  data  select- gt fetch        id    data  id     column    data  column     column   preg replace     a-zA-Z0-9            column     remove all special characters   update    con- gt prepare  UPDATE table SET column  column WHERE id   id      update- gt bindParam   column    column     update- gt execute        echo  column   lt br gt

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I have written this UDF  However  it only trims special characters at the beginning of the string  It also converts the string to lower case  You can update this function if desired   DELIMITER     DROP FUNCTION IF EXISTS DELETE DOUBLE SPACES    CREATE FUNCTION DELETE DOUBLE SPACES   title VARCHAR 250    RETURNS VARCHAR 250  DETERMINISTIC BEGIN     DECLARE result VARCHAR 250       SET result   REPLACE  title                   WHILE  result  lt  gt  title  DO          SET title   result          SET result   REPLACE  title                   END WHILE      RETURN result  END    DROP FUNCTION IF EXISTS LFILTER    CREATE FUNCTION LFILTER   title VARCHAR 250    RETURNS VARCHAR 250  DETERMINISTIC BEGIN     WHILE  1 1  DO         IF   ASCII title  BETWEEN ASCII  a   AND ASCII  z               OR ASCII title  BETWEEN ASCII  A   AND ASCII  Z               OR ASCII title  BETWEEN ASCII  0   AND ASCII  9             THEN             SET title   LOWER  title                SET title   REPLACE                  REPLACE                      REPLACE                          title                          CHAR 10                                                  CHAR 13                                           CHAR 9                                  SET title   DELETE DOUBLE SPACES  title                RETURN title          ELSE             SET title   SUBSTRING  title  2                      END IF      END WHILE  END   DELIMITER    SELECT LFILTER          amp      1a    b      Also  you could use regular expressions but this requires installing a MySql extension

User · Answer

Probably a silly suggestion compared to others   if  preg match     a-zA-Z0-9      string         sortedString preg replace     a-zA-Z0-9          string

User · Answer

Needed to replace non-alphanumeric characters rather than remove non-alphanumeric characters so I have created this based on Ryan Shillington s alphanum  Works for strings up to 255 characters in length  DROP FUNCTION IF EXISTS alphanumreplace   DELIMITER    CREATE FUNCTION alphanumreplace  str CHAR 255   d CHAR 32    RETURNS CHAR 255   BEGIN    DECLARE i  len SMALLINT DEFAULT 1     DECLARE ret CHAR 32  DEFAULT        DECLARE c CHAR 1      SET len   CHAR LENGTH  str       REPEAT      BEGIN        SET c   MID  str  i  1           IF c REGEXP     alnum     THEN SET ret CONCAT ret c          ELSE SET ret CONCAT ret d         END IF         SET i   i   1       END     UNTIL i  gt  len END REPEAT     RETURN ret   END    DELIMITER      Example   select  hello world   alphanum  hello world    alphanumreplace  hello world    -     -------------- -------------------------- -------------------------------------    hello world    alphanum  hello world      alphanumreplace  hello world    -      -------------- -------------------------- -------------------------------------    hello world    helloworld                 hello-world-                           -------------- -------------------------- -------------------------------------    You ll need to add the alphanum function seperately if you want that  I just have it here for the example

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So far  the only alternative approach less complicated than the other answers here is to determine the full set of special characters of the column  i e  all the special characters that are in use in that column at the moment  and then do a sequential replace of all those characters  e g   update pages set slug   lower replace replace replace replace name             -                    amp            replacing just space  -      amp  only         This is only advisable on a known set of data  otherwise it s   trivial for some special characters to slip past with a   blacklist approach instead of a whitelist approach    Obviously  the simplest way is to pre-validate the data outside of sql due to the lack of robust built-in whitelisting  e g  via a regex replace

User · Answer

Based on the answer by Ryan Shillington  modified to work with strings longer than 255 characters and preserving spaces from the original string    FYI there is lower str  in the end   I used this to compare strings   DROP FUNCTION IF EXISTS spacealphanum  DELIMITER    CREATE FUNCTION  spacealphanum   str TEXT   RETURNS TEXT CHARSET utf8 BEGIN    DECLARE i  len SMALLINT DEFAULT 1     DECLARE ret TEXT DEFAULT        DECLARE c CHAR 1      SET len   CHAR LENGTH  str       REPEAT      BEGIN        SET c   MID  str  i  1           IF c REGEXP     alnum     THEN          SET ret CONCAT ret c          ELSEIF  c       THEN           SET ret CONCAT ret             END IF         SET i   i   1       END     UNTIL i  gt  len END REPEAT     SET ret   lower ret     RETURN ret     END      DELIMITER

User · Answer

Be careful  characters like     or    are considered as alpha by MySQL  It better to use something like       IF c BETWEEN  a  AND  z  OR c BETWEEN  A  AND  Z  OR c BETWEEN  0  AND    9  OR c    -  THEN

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The fastest way I was able to find  and using   is with convert     from Doc  CONVERT   with USING is used to convert data between different character sets   Example   convert string USING ascii    In your case the right character set will be self defined  NOTE from Doc  The USING form of CONVERT   is available as of 4 1 0

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the alphanum function  self answered  have a bug  but I don t know why  For text  cas synt ls 75W140 1L  return  cassyntls75W1401    L  from the end is missing some how   Now I use   delimiter    DROP FUNCTION IF EXISTS alphanum    CREATE FUNCTION alphanum prm strInput varchar 255   RETURNS VARCHAR 255  DETERMINISTIC BEGIN   DECLARE i INT DEFAULT 1    DECLARE v char VARCHAR 1     DECLARE v parseStr VARCHAR 255  DEFAULT      WHILE  i  lt   LENGTH prm strInput     DO   SET v char   SUBSTR prm strInput i 1     IF v char REGEXP     A-Za-z0-9     THEN          SET v parseStr   CONCAT v parseStr v char       END IF    SET i   i   1  END WHILE  RETURN trim v parseStr   END       found on google

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I had a similar problem with trying to match last names in our database that were slightly different   For example  sometimes people entered the same person s name as  McDonald  and also as  Mc Donald   or  St John  and  St  John    Instead of trying to convert the Mysql data  I solved the problem by creating a function  in PHP  that would take a string and create an alpha-only regular expression   function alpha only regex  str         alpha only   str split preg replace     A-Z  i        str        return     a-zA-Z    implode    a-zA-Z      alpha only     a-zA-Z          Now I can search the database with a query like this    lastname regex   alpha only regex  lastname    query    SELECT   FROM my table WHERE lastname REGEXP   lastname regex

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Straight and battletested solution for latin and cyrillic characters   DELIMITER     CREATE FUNCTION  remove non numeric and letters  input TEXT    RETURNS TEXT   BEGIN     DECLARE output TEXT DEFAULT         DECLARE iterator INT DEFAULT 1      WHILE iterator  lt   LENGTH input    1  DO       IF SUBSTRING input  iterator  1  IN            0    1    2    3    4    5    6    7    8    9    A    B    C    D    E    F    G    H    I    J    K    L    M    N    O    P    Q    R    S    T    U    V    W    X    Y    Z    a    b    c    d    e    f    g    h    i    j    k    l    m    n    o    p    q    r    s    t    u    v    w    x    y    z                                                                                                                                                                                                                                                                                                                                         THEN         SET output   CONCAT output  SUBSTRING input  iterator  1          END IF        SET iterator   iterator   1      END WHILE      RETURN output    END     DELIMITER     Usage   -- outputs  hello12356  SELECT remove non numeric and letters  hello - 12356-

User · Answer

None of these answers worked for me   I had to create my own function called alphanum which stripped the chars for me   DROP FUNCTION IF EXISTS alphanum   DELIMITER    CREATE FUNCTION alphanum  str CHAR 255    RETURNS CHAR 255  DETERMINISTIC BEGIN    DECLARE i  len SMALLINT DEFAULT 1     DECLARE ret CHAR 255  DEFAULT        DECLARE c CHAR 1     IF str IS NOT NULL THEN      SET len   CHAR LENGTH  str         REPEAT        BEGIN          SET c   MID  str  i  1             IF c REGEXP     alnum     THEN            SET ret CONCAT ret c            END IF           SET i   i   1         END       UNTIL i  gt  len END REPEAT     ELSE     SET ret       END IF    RETURN ret   END    DELIMITER      Now I can do   select  This works finally    alphanum  This works finally       and I get    --------------------- ---------------------------------    This works finally    alphanum  This works finally       --------------------- ---------------------------------    This works finally    Thisworksfinally                   --------------------- ---------------------------------  1 row in set  0 00 sec    Hurray

User · Answer

I tried a few solutions but at the end used replace  My data set is part numbers and I fairly know what to expect  But just for sanity  I used PHP to build the long query    dirty   array       -                                   amp           query    part no   foreach   dirty as  dirt         query    replace  query   dirt          echo  query    This outputs something I used to get a headache from   replace replace replace replace replace replace replace replace replace replace part no          -                                                        amp

User · Answer

This can be done with a regular expression replacer function I posted in another answer and have blogged about here  It may not be the most efficient solution possible and might look overkill for the job in hand - but like a Swiss army knife  it may come in useful for other reasons   It can be seen in action removing all non-alphanumeric characters in this Rextester online demo   SQL  excluding the function code for brevity    SELECT txt         reg replace txt                        a-zA-Z0-9                                               TRUE                     0                     0                      AS  reg replaced  FROM test

User · Answer

Since MySQL 8 0 you can use regular expression to remove non alphanumeric characters from a string  There is method REGEXP REPLACE  Here is the code to remove non-alphanumeric characters   UPDATE  table  SET  column    REGEXP REPLACE  column      0-9a-zA-Z

User · Answer

I needed to get only alphabetic characters of a string in a procedure  and did   SET  source    whatever you want   SET  target       SET  i   1  SET  len   LENGTH  source   WHILE  i  lt    len DO     SET  char   SUBSTRING  source   i  1       IF   ORD  char   gt   65  amp  amp  ORD  char   lt   90      ORD  char   gt   97  amp  amp  ORD  char   lt   122   THEN         SET  target   CONCAT  target   char       END IF      SET  i    i   1  END WHILE

[mysql] How to remove all non-alpha numeric characters from a string in MySQL?

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