# How to measure distance between strings? What is Levenstein Distance?

Random | 12 Sep 2014
Tags: mysql, database, levenshtein-distance, fuzzy-text-search

Levenshtein distance function can be used to measure distance between the strings. Smaller distance will mean that string 1 is closer to string 2. This function can be used to implement "fuzzy" text search in mySQL where you can search for records and order by levenshtein distance in ascending order. In this case the closest matches (more relevant results) will appear on top and then the less relevant ones.

DELIMITER ;;
DROP FUNCTION IF EXISTS levenshtein;;
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 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 ;