CREATE OR REPLACE FUNCTION dld -- DamerauLevenshtein distance
  (str1              VARCHAR2 DEFAULT NULL,
   str2              VARCHAR2 DEFAULT NULL)
  RETURN NUMBER DETERMINISTIC
AS
  lenStr1            NUMBER := NVL (LENGTH (str1), 0);
  lenStr2            NUMBER := NVL (LENGTH (str2), 0);
  TYPE mytabtype IS  TABLE OF NUMBER INDEX BY BINARY_INTEGER;
  TYPE myarray IS    TABLE OF mytabtype INDEX BY BINARY_INTEGER;
  d                  myarray;
  cost               NUMBER := 0;
BEGIN
  IF str1 = str2 THEN
    RETURN 0;
  ELSIF lenStr1 = 0 OR lenStr2 = 0 THEN
    RETURN GREATEST (lenStr1, lenStr2);
  ELSIF lenStr1 = 1 AND lenStr2 = 1 AND str1 <> str2 THEN
    RETURN 1;
  ELSE
    FOR j in 0 .. lenStr2 LOOP
      d (0) (j) := j;
    END LOOP;
    FOR i in 1 .. lenStr1 LOOP
      d (i) (0) := i;
      FOR j in 1 .. lenStr2 LOOP
        IF SUBSTR (str1, i, 1) = SUBSTR (str2, j, 1) THEN
          cost := 0;
        ELSE
          cost := 1;
        END IF;
        d (i) (j) := LEAST (
                              d (i-1) (j)   + 1,      -- deletion
                              d (i)   (j-1) + 1,      -- insertion
                              d (i-1) (j-1) + cost    -- substitution
                           );
        IF i > 1 AND j > 1
           AND SUBSTR (str1, i,   1) = SUBSTR (str2, j-1, 1)
           AND SUBSTR (str1, i-1, 1) = SUBSTR (str2, j,   1)
        THEN
          d (i) (j) := LEAST (
                                d (i)   (j),      
                                d (i-2) (J-2) + cost  -- transposition
                             );
        END IF;              
      END LOOP;
    END LOOP;
    RETURN d (lenStr1) (lenStr2);
  END IF;
END dld;
/

SCOTT@orcl_11gR2> select utl_match.edit_distance ('grep', 'gerp')
  2  	      as "Levenshtein",
  3  	    dld ('grep', 'gerp')
  4  	      as "Damereau-Levenshtein"
  5  from   dual
  6  /

Levenshtein Damereau-Levenshtein
----------- --------------------
          2                    1

1 row selected.

SCOTT@orcl_11gR2> 

Errors = 1
Misspelled words:
futur
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