Levenshtein Distance Algorithm: Oracle PL/SQL Implementation

Levenshtein Distance Algorithm: Oracle PL/SQL Implementation

by Barbara Boehmer ([email protected])

sql 代码

CREATE OR REPLACE FUNCTION ld -- Levenshtein distance
  (p_source_string   IN VARCHAR2,
   p_target_string   IN VARCHAR2)
  RETURN                NUMBER
  DETERMINISTIC
AS
  v_length_of_source    NUMBER := NVL (LENGTH (p_source_string), 0);
  v_length_of_target    NUMBER := NVL (LENGTH (p_target_string), 0);
  TYPE mytabtype IS     TABLE OF NUMBER INDEX BY BINARY_INTEGER;
  column_to_left        mytabtype;
  current_column        mytabtype;
  v_cost                NUMBER := 0;
BEGIN
  IF v_length_of_source = 0 THEN
    RETURN v_length_of_target;
  ELSIF v_length_of_target = 0 THEN
    RETURN v_length_of_source;
  ELSE
    FOR j IN 0 .. v_length_of_target LOOP
      column_to_left(j) := j;
    END LOOP;
    FOR i IN 1.. v_length_of_source LOOP
      current_column(0) := i;
      FOR j IN 1 .. v_length_of_target LOOP
        IF SUBSTR (p_source_string, i, 1) =
           SUBSTR (p_target_string, j, 1)
        THEN v_cost := 0;
        ELSE v_cost := 1;
        END IF;
        current_column(j) := LEAST (current_column(j-1) + 1,
                                    column_to_left(j) + 1,
                                    column_to_left(j-1) + v_cost);
      END LOOP;
      FOR j IN 0 .. v_length_of_target  LOOP
        column_to_left(j) := current_column(j);
      END LOOP;
    END LOOP;
  END IF;
  RETURN current_column(v_length_of_target);
END ld;