## Levenshtein distance

### from the Artful Common Queries page

 The Levenshtein distance between two strings is the minimum number of operations needed to transform one string into the other, where an operation may be insertion, deletion or substitution of one character. Jason Rust published this MySQL algorithm for it at http://www.codejanitor.com/wp/. ```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; -- max strlen=255 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; ``` Helper function: ``` CREATE FUNCTION levenshtein_ratio( s1 VARCHAR(255), s2 VARCHAR(255) ) RETURNS INT DETERMINISTIC BEGIN DECLARE s1_len, s2_len, max_len INT; SET s1_len = LENGTH(s1), s2_len = LENGTH(s2); IF s1_len > s2_len THEN SET max_len = s1_len; ELSE SET max_len = s2_len; END IF; RETURN ROUND((1 - LEVENSHTEIN(s1, s2) / max_len) * 100); END; ```Last updated 22 May 2009 