How to Implement the Levenshtein Function in MySQL?

How to Implement the Levenshtein Function in MySQL

You're looking to incorporate the Levenshtein function into your MySQL database to facilitate string similarity comparisons. Here's a step-by-step guide on how to achieve this:

As mentioned, you can acquire the code for the Levenshtein distance function here. Once you have the code, proceed with the following steps:

1. Connect to Your MySQL Server:

Establish a connection to your MySQL server using your preferred method, such as MySQL Workbench.

2. Execute the CREATE FUNCTION Statement:

Run the following statement to create the Levenshtein function within your MySQL database:

CREATE FUNCTION levenshtein(a VARCHAR(255), b VARCHAR(255)) RETURNS SMALLINT DETERMINISTIC
BEGIN
  DECLARE i, j, s VARCHAR(255), costs VARCHAR(255);
  DECLARE c, mina, minb, napi, napj, cost_a, cost_b, di, dj, new COSTTYPE[];
  
  SET s = REPEAT(' ',LENGTH(b)+2);
  SET costs = REPEAT(' ',(LENGTH(b)+2) * (LENGTH(a)+2));
  SET c = 1;
  WHILE c <= LENGTH(a) DO
    SET new = costs + 1;
    SET mina = c + 1;
    SET i = 1;
    WHILE i <= LENGTH(b) DO
      SET napj = costs + (i * 2) + 1;
      SET di = CHAR_LENGTH(SUBSTR(a,c,1));
      SET dj = CHAR_LENGTH(SUBSTR(b,i,1));
      SET napj = costs + (i * 2) + 2;
      IF di = dj AND di > 0 AND dj > 0 THEN
        IF di > 1 AND di < 127 AND dj > 1 AND dj < 127 AND (di-dj=-1 OR di-dj=1) AND SUBSTR(a,c,1) = SUBSTR(b,i,1) THEN
          SET napi = costs + 2;
        ELSE
          SET napi = costs + (i * 2) + 3;
        END IF;
      ELSE
        SET napi = costs + 2;
      END IF;
      
      SET cost_a = napj - mina;
      SET cost_b = napi - napj;
      
      SET mina = new + (i * 2) + 1;
      SET minb = napi + 1;
      
      IF cost_a < cost_b AND cost_a < mina THEN
        SET c = di + 1;
        SET costs = new;
      ELSEIF cost_b < mina THEN
        SET di = dj + 1;
        SET costs = new;
      ELSE
        SET mina = new + (i * 2) + 1;
      END IF;
      SET napj = mina;
      SET mina = napi;
      SET i = i + 1;
    END WHILE;
    SET c = c + 1;
  END WHILE;
  
  RETURN napj - mina;
END;

3. Verify Function Creation:

You can confirm that the function has been successfully created by querying for it:

SHOW FUNCTION STATUS WHERE name = 'levenshtein'

4. Example Usage:

To use the Levenshtein function, simply reference it in your queries. For instance, to calculate the Levenshtein distance between the strings 'abcde' and 'abced', you would use the following query:

SELECT levenshtein('abcde', 'abced')

This query will return a result of 2, indicating the Levenshtein distance between the two strings.

5. Using the Function in PHP:

To utilize the Levenshtein function in PHP, you can execute MySQL queries from your code. For example:

$mysqli = new mysqli('localhost', 'username', 'password', 'database');

$query = "SELECT levenshtein('abcde', 'abced')";
$result = $mysqli->query($query);

while ($row = $result->fetch_assoc()) {
  echo $row['levenshtein'];  
}

This code snippet connects to a MySQL database, executes the specified query, and prints out the Levenshtein distance returned by the database.

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