Levenshtein Distance

The Levenshtein distance between two words is the minimum number of single-character edits (insertion, deletion, substitution) required to change one word into the other. – Wikipedia

To implement in MySQL, use the following function – if using phpmyadmin you will need to set a different delimiter such as ‘$’ instead of ‘;’ to create this function.

CREATE FUNCTION levenshtein( s1 VARCHAR(255), s2 VARCHAR(255) ) 
  RETURNS INT 
  DETERMINISTIC 
  BEGIN 
    DECLARE s1len, s2len, i, j, c, ctemp, cost INT; 
    DECLARE s1char CHAR; 
    -- max strlen=255 

    DECLARE cv0, cv1 VARBINARY(256); 
    SET s1len = CHARLENGTH(s1), s2len = CHARLENGTH(s2), cv1 = 0x00, j = 1, i = 1, c = 0; 
    IF s1 = s2 THEN 
      RETURN 0; 
    ELSEIF s1len = 0 THEN 
      RETURN s2len; 
    ELSEIF s2len = 0 THEN 
      RETURN s1len; 
    ELSE 
      WHILE j <= s2len DO 
        SET cv1 = CONCAT(cv1, UNHEX(HEX(j))), j = j + 1; 
      END WHILE; 
      WHILE i <= s1len DO 
        SET s1char = SUBSTRING(s1, i, 1), c = i, cv0 = UNHEX(HEX(i)), j = 1; 
        WHILE j <= s2len DO 
          SET c = c + 1; 
          IF s1char = SUBSTRING(s2, j, 1) THEN

            SET cost = 0; ELSE SET cost = 1; 
          END IF; 
          SET ctemp = CONV(HEX(SUBSTRING(cv1, j, 1)), 16, 10) + cost; 
          IF c > ctemp THEN SET c = ctemp; END IF; 
            SET ctemp = CONV(HEX(SUBSTRING(cv1, j+1, 1)), 16, 10) + 1; 
            IF c > ctemp 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;
  

-Artful Software

The following is example usage – it returns the name column ordered by the Levenshtein distance – the lowest number is the closest match.

SELECT name, LEVENSHTEIN(name, 'string') AS distance 
        FROM table ORDER BY distance ASC