My sql function to count similar words in comma seperated string

mysql-function.sql

DROP FUNCTION IF EXISTS SPLIT_STRING;
DROP FUNCTION IF EXISTS SIMILAR_WORDS;

DELIMITER $$

CREATE FUNCTION SPLIT_STRING(str VARCHAR(255), delim VARCHAR(12), pos INT)
  RETURNS VARCHAR(255)
  RETURN REPLACE(SUBSTRING(SUBSTRING_INDEX(str, delim, pos),
       LENGTH(SUBSTRING_INDEX(str, delim, pos-1)) + 1),
       delim, '');
END$$ 

DELIMITER ;

DELIMITER $$

CREATE FUNCTION SIMILAR_WORDS( s1 VARCHAR(255), s2 VARCHAR(255) ) 
  RETURNS INT 
  DETERMINISTIC 
  BEGIN 
    -- decalre variables
    DECLARE s1_len, s2_len, words_len1, words_len2, i, j, c INT; 
    DECLARE s1_char, s2_char,temp VARCHAR(255); 
    -- max strlen=255 

    SET s1_len = CHAR_LENGTH(s1), s2_len = CHAR_LENGTH(s2), j = 0, i = 0, c = 0; 
    IF s1 = s2 THEN 
      RETURN 10; 
    ELSEIF s1_len = 0 THEN 
      RETURN s1_len; 
    ELSEIF s2_len = 0 THEN 
      RETURN s2_len; 
    ELSE 
      SET words_len1 = (LENGTH(s1) - LENGTH(REPLACE(s1, ',', ''))) + 1; 
      SET words_len2 = (LENGTH(s2) - LENGTH(REPLACE(s2, ',', ''))) + 1; 

      IF words_len2 > words_len1 THEN
        SET words_len1 = words_len1 + words_len2;
        SET words_len2 = words_len1 - words_len2;
        SET words_len1 = words_len1 - words_len2;
        SET temp = s1;
        SET s1 = s2;
        SET s2 = temp; 
      END IF;

      WHILE i < words_len1 DO
        WHILE j < words_len2 DO
          SET s1_char = TRIM(SPLIT_STRING(s1, ',', i+1));
          SET s2_char = TRIM(SPLIT_STRING(s2, ',', j+1));
          IF STRCMP(s1_char, s2_char) = 0 THEN
            SET c = c + 1;
          END IF;
          SET j = j + 1;
        END WHILE;
        SET i = i + 1;    
        SET j = 0;    
      END WHILE;
    END IF; 
    RETURN c; 
END$$ 

DELIMITER ;

--usage: select SIMILAR_WORDS('Apple,Orange,Lemon,Banana', 'Lemon,Orange')