70 lines
1.8 KiB
MySQL
70 lines
1.8 KiB
MySQL
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-- Levenshtein function
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-- Source: https://openquery.com.au/blog/levenshtein-mysql-stored-function
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-- Levenshtein reference: http://en.wikipedia.org/wiki/Levenshtein_distance
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-- Arjen note: because the levenshtein value is encoded in a byte array, distance cannot exceed 255;
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-- thus the maximum string length this implementation can handle is also limited to 255 characters.
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DELIMITER $$
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DROP FUNCTION IF EXISTS LEVENSHTEIN $$
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CREATE FUNCTION LEVENSHTEIN(s1 VARCHAR(255) CHARACTER SET utf8, s2 VARCHAR(255) CHARACTER SET utf8)
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RETURNS INT
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DETERMINISTIC
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BEGIN
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DECLARE s1_len, s2_len, i, j, c, c_temp, cost INT;
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DECLARE s1_char CHAR CHARACTER SET utf8;
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-- max strlen=255 for this function
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DECLARE cv0, cv1 VARBINARY(256);
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SET s1_len = CHAR_LENGTH(s1),
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s2_len = CHAR_LENGTH(s2),
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cv1 = 0x00,
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j = 1,
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i = 1,
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c = 0;
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IF (s1 = s2) THEN
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RETURN (0);
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ELSEIF (s1_len = 0) THEN
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RETURN (s2_len);
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ELSEIF (s2_len = 0) THEN
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RETURN (s1_len);
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END IF;
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WHILE (j <= s2_len) DO
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SET cv1 = CONCAT(cv1, CHAR(j)),
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j = j + 1;
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END WHILE;
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WHILE (i <= s1_len) DO
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SET s1_char = SUBSTRING(s1, i, 1),
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c = i,
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cv0 = CHAR(i),
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j = 1;
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WHILE (j <= s2_len) DO
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SET c = c + 1,
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cost = IF(s1_char = SUBSTRING(s2, j, 1), 0, 1);
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SET c_temp = ORD(SUBSTRING(cv1, j, 1)) + cost;
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IF (c > c_temp) THEN
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SET c = c_temp;
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END IF;
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SET c_temp = ORD(SUBSTRING(cv1, j+1, 1)) + 1;
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IF (c > c_temp) THEN
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SET c = c_temp;
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END IF;
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SET cv0 = CONCAT(cv0, CHAR(c)),
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j = j + 1;
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END WHILE;
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SET cv1 = cv0,
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i = i + 1;
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END WHILE;
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RETURN (c);
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END $$
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DELIMITER ;
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