how to compute similarity between two strings in MYSQL

Question

if i have two strings in mysql:

 @a="Welcome to Stack Overflow" @b=" Hello to stack overflow"; 

is there a way to get the similarity percentage between those two string using MYSQL? here for example 3 words are similar and thus the similarity should be something like:
count(similar words between @a and @b) / (count(@a)+count(@b) - count(intersection))
and thus the result is 3/(4 + 4 - 3)= 0.6
any idea is highly appreciated!

Answer 1

you can use this function (cop^H^H^Hadapted from http://www.artfulsoftware.com/infotree/queries.php#552):

CREATE FUNCTION `levenshtein`( s1 text, s2 text) RETURNS int(11)     DETERMINISTIC BEGIN      DECLARE s1_len, s2_len, i, j, c, c_temp, cost INT;      DECLARE s1_char CHAR;      DECLARE cv0, cv1 text;      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 

and for getting it as XX% use this function

CREATE FUNCTION `levenshtein_ratio`( s1 text, s2 text ) RETURNS int(11)     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