How to Add a Levenshtein Distance Function to MySQL?

Adding the Levenshtein Function to MySQL

Introduction:

Calculating the Levenshtein distance, a metric for string similarity, is a valuable tool in various applications. This article guides you through the process of adding the Levenshtein function to MySQL, enabling you to easily determine the similarity between strings within your database queries.

Adding the Function:

To add the Levenshtein function to MySQL, follow these steps:

1. Connect to MySQL: Establish a connection to your MySQL server using a tool such as MySQL Workbench or the command line.

2. Run the following SQL statement:

   CREATE FUNCTION levenshtein(s1 VARCHAR(255), s2 VARCHAR(255)) RETURNS INT
   DETERMINISTIC
   BEGIN
       DECLARE len1 INT;
       DECLARE len2 INT;
       DECLARE i INT;
       DECLARE j INT;
       DECLARE cost INT;
       DECLARE min1 INT;
       DECLARE min2 INT;
       DECLARE min3 INT;
   
       SET len1 = LENGTH(s1);
       SET len2 = LENGTH(s2);
   
       DECLARE matrix INT[][];
       SET matrix = NEW INT[len1 + 1][len2 + 1];
   
       FOR i = 0 TO len1 DO
           SET matrix[i][0] = i;
       END FOR;
   
       FOR j = 0 TO len2 DO
           SET matrix[0][j] = j;
       END FOR;
   
       FOR i = 1 TO len1 DO
           FOR j = 1 TO len2 DO
               IF s1[i] = s2[j] THEN
                   SET cost = 0;
               ELSE
                   SET cost = 1;
               END IF;
   
               SET min1 = matrix[i - 1][j] + 1;
               SET min2 = matrix[i][j - 1] + 1;
               SET min3 = matrix[i - 1][j - 1] + cost;
   
               IF min1 < min2 THEN
                   SET min2 = min1;
               END IF;
   
               IF min2 < min3 THEN
                   SET min3 = min2;
               END IF;
   
               SET matrix[i][j] = min3;
           END FOR;
       END FOR;
   
       RETURN matrix[len1][len2];
   END

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3. Verify Function Creation: Execute a query to ensure the function has been successfully added:

   SELECT levenshtein('abcde', 'abced');

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   You should get the expected result of 2, indicating the distance between the two strings.

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