regex - 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 ?

Answer 1

Using MySQL 8.0 or higher

Courtesy of michal.jakubeczy's answer below, replacing by Regex is now supported by MySQL:

UPDATE {table} SET {column} = REGEXP_REPLACE({column}, '[^0-9a-zA-Z ]', '')

Using MySQL 5.7 or lower

Regex isn't supported here. 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 > 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!