Compara Frases o palabras similares en php y mysql (levenshtein)

 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
 

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