Removing the special chaters from a string using user defined function using PHP

1) Function
DELIMITER //
CREATE DEFINER=`platformuser`@`localhost` FUNCTION `fn_RemoveSpecialChars`(`pString` CHAR(50)) RETURNS char(50) CHARSET latin1
    DETERMINISTIC
BEGIN
  DECLARE i, len SMALLINT DEFAULT 1;
  DECLARE CleanString varchar(1000) DEFAULT '';
  DECLARE c CHAR(1);
  DECLARE regx INT(1);

  IF pString IS NULL
  THEN
    RETURN "";
  END IF;

  SET len = LENGTH( pString );
  REPEAT
    BEGIN
      SET c = MID( pString, i, 1 );
      SELECT c REGEXP '[^a-zA-Z0-9 /t/-/_]' into regx;
     
      IF c="" THEN
          SET CleanString=CONCAT(CleanString,' ');
      ELSEIF regx =0 THEN
        SET CleanString=CONCAT(CleanString,c);
      END IF;    
     
      SET i = i + 1;
    END;
  UNTIL i > len END REPEAT;
   RETURN CleanString;
END//
DELIMITER ;

---------------------------------------------------------------------------
output

 SELECT fn_RemoveSpecialChars('welcone world !#@#@');

 Result: welcome world