title: Slow Performance of Levenshtein distance formula in big database
body: <p>I used this query for searching company details</p>
  
  <pre><code>select * 
  from company_details 
  where levenshtein_ratio('New York Life Insurance Company',`cmp_name`) &gt; 50 
  </code></pre>
  
  <p>company_details table has more than 1 million records</p>
  
  <p>But it is too slow it gets records after 1 or 2 minutes some time.</p>
  
  <p>My Levenshtein function is:</p>
  
  <pre><code>BEGIN
      DECLARE s1_len, s2_len, i, j, c, c_temp, cost INT;
      DECLARE s1_char CHAR;
          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 &lt;= s2_len DO
          SET cv1 = CONCAT(cv1, UNHEX(HEX(j))), j = j + 1;
        END WHILE;
        WHILE i &lt;= s1_len DO
          SET s1_char = SUBSTRING(s1, i, 1), c = i, cv0 = UNHEX(HEX(i)), j = 1;
          WHILE j &lt;= 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 &gt; c_temp THEN SET c = c_temp; END IF;
              SET c_temp = CONV(HEX(SUBSTRING(cv1, j+1, 1)), 16, 10) + 1;
              IF c &gt; 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
  </code></pre>
  
  <p>and ratio function:</p>
  
  <pre><code>BEGIN 
      DECLARE s1_len, s2_len, max_len INT; 
      SET s1_len = LENGTH(s1), s2_len = LENGTH(s2); 
      IF s1_len &gt; s2_len THEN  
        SET max_len = s1_len;  
      ELSE  
        SET max_len = s2_len;  
      END IF; 
      RETURN ROUND((1 - LEVENSHTEIN(s1, s2) / max_len) * 100); 
    END
  </code></pre>