OLD VERSION

FUNCTION MOST_RECENT_DATE_4
(a IN DATE, 
b IN DATE, 
c IN DATE, 
d IN DATE)
RETURN DATE IS
BEGIN 
   IF a > b THEN -- a,c,d
      IF a > c THEN -- a,d
         IF a > d THEN
            RETURN a;
         ELSE
            RETURN d;
         END IF;
      ELSE -- c,d
         IF c > d THEN
            RETURN c;
         ELSE
            RETURN d;
         END IF;
      END IF;
   ELSE -- b,c,d
      IF b > c THEN -- b,d
         IF b > d THEN
            RETURN b;
         ELSE
            RETURN d;
         END IF;
      ELSE -- c,d
          IF c > d THEN
             RETURN c;
          ELSE
             RETURN d;
          END IF;
      END IF;
   END IF;
   return null;
EXCEPTION WHEN OTHERS THEN
	raise_application_error(-20001,'An error occurred in MOST_RECENT_DATE_4 - '|| SQLCODE || ' -ERROR- ' || SQLERRM);
END;

NEW VERSION

FUNCTION MOST_RECENT_DATE_4
(ain IN DATE, 
bin IN DATE, 
cin IN DATE, 
din IN DATE)
RETURN DATE IS
   a DATE;
   b DATE;
   c DATE;
   d DATE;
BEGIN 
   IF ain is null THEN
      a := to_date('1.4.2000','DD.MM.YYYY');
   ELSE
      a := ain;
   END IF;
   IF bin is null THEN
      b := to_date('1.4.2000','DD.MM.YYYY');
   ELSE
      b := bin;
   END IF;
   IF cin is null THEN
      c := to_date('1.4.2000','DD.MM.YYYY');
   ELSE
      c := cin;
   END IF;
   IF din is null THEN
      d := to_date('1.4.2000','DD.MM.YYYY');
   ELSE
      d := din;
   END IF;
   IF a > b THEN -- a,c,d
      IF a > c THEN -- a,d
         IF a > d THEN
            RETURN a;
         ELSE
            RETURN d;
         END IF;
      ELSE -- c,d
         IF c > d THEN
            RETURN c;
         ELSE
            RETURN d;
         END IF;
      END IF;
   ELSE -- b,c,d
      IF b > c THEN -- b,d
         IF b > d THEN
            RETURN b;
         ELSE
            RETURN d;
         END IF;
      ELSE -- c,d
          IF c > d THEN
             RETURN c;
          ELSE
             RETURN d;
          END IF;
      END IF;
   END IF;
   return null;
EXCEPTION WHEN OTHERS THEN
	raise_application_error(-20001,'An error occurred in MOST_RECENT_DATE_4 - '|| SQLCODE || ' -ERROR- ' || SQLERRM);
END;