SELECT SOUNDEX('string');

SELECT SOUNDEX('Hello'), SOUNDEX('Halle');

+-----------------+-----------------+
| SOUNDEX('Hello') | SOUNDEX('Halle')|
+-----------------+-----------------+
| H400            | H400            |
+-----------------+-----------------+

SELECT SOUNDEX('string1') = SOUNDEX('string2');

SELECT SOUNDEX('Hello') = SOUNDEX('Halle');

CREATE FUNCTION `levenshtein`(s1 VARCHAR(255), s2 VARCHAR(255)) RETURNS int(11)
    DETERMINISTIC
    BEGIN
        DECLARE s1_len, s2_len, i, j, c, c_temp, cost INT;
        DECLARE s1_char CHAR;
        DECLARE cv0, cv1 VARCHAR(255);
        SET s1_len = CHAR_LENGTH(s1), s2_len = CHAR_LENGTH(s2), cv1 = 0x00, j = 1, i = 1, c = 0;
        IF s1 = s2 THEN
            RETURN 0;
        ELSEIF s1_len = 0 THEN
            RETURN s2_len;
        ELSEIF s2_len = 0 THEN
            RETURN s1_len;
        ELSE
            WHILE j <= s2_len DO
                SET cv1 = CONCAT(cv1, UNHEX(HEX(j))), j = j + 1;
            END WHILE;
            WHILE i <= s1_len DO
                SET s1_char = SUBSTRING(s1, i, 1), c = i, cv0 = UNHEX(HEX(i)), j = 1;
                WHILE j <= s2_len DO
                    SET c = c + 1;
                    IF s1_char = SUBSTRING(s2, j, 1) THEN SET cost = 0;
                    ELSE SET cost = 1;
                    END IF;
                    SET c_temp = CONV(HEX(SUBSTRING(cv1, j, 1)), 16, 10) + cost;
                    IF c > c_temp THEN SET c = c_temp;
                    END IF;
                    SET cv1 = CONCAT(cv1, UNHEX(HEX(c))), j = j + 1;
                END WHILE;
                SET cv_tmp = cv0, cv0 = cv1, cv1 = cv_tmp, i = i + 1;
            END WHILE;
        END IF;
        RETURN c;
    END

SELECT levenshtein('string1', 'string2');