Levenshtein function for (My)SQL

Levenshtein-function.sql

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