mysql-function-levenshtein.sql

DROP FUNCTION IF EXISTS levenshtein;

DELIMITER //

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;
//

DELIMITER ;