mysql_levenshtein_function.sql

DELIMITER $$
CREATE FUNCTION LEVENSHTEIN( s1 VARCHAR(255), s2 VARCHAR(255) )
RETURNS INT
DETERMINISTIC
BEGIN
DECLARE s1_len, s2_len, i, j, c, c_temp, cost INT;
DECLARE s1_char CHAR;

DECLARE cv0, cv1 VARBINARY(256);
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 c_temp = CONV(HEX(SUBSTRING(cv1, j+1, 1)), 16, 10) + 1;
            IF c > c_temp THEN
                SET c = c_temp;
            END IF;
            SET cv0 = CONCAT(cv0, UNHEX(HEX(c))), j = j + 1;
        END WHILE;
        SET cv1 = cv0, i = i + 1;
    END WHILE;
END IF;
RETURN c;
END$$
DELIMITER;