Number of working Days (Mon-Fri) between two dates?

[jmodic]

The following might be considered "more elegant" (that in fact is a matter of taste), but probably not "quicker" as it actualy selects rows from the database. Anyway:

CREATE OR REPLACE FUNCTION working_days
  (p_start_date DATE,
   p_end_date DATE)
RETURN NUMBER
IS
  v_result NUMBER;
BEGIN
  SELECT SUM(DECODE(DAY, '7', 0, '6', 0, 1))
  INTO v_result
  FROM 
  (SELECT TO_NUMBER(TO_CHAR(p_start_date + row_num,'D')) AS DAY
   FROM 
    (SELECT ROWNUM-1 AS row_num FROM ALL_OBJECTS
     WHERE ROWNUM < TRUNC(p_end_date+1) - TRUNC(p_start_date-1)));
  RETURN v_result;
END;

Of course the day-of-the-week numbers might be different for Sat-Sun on your system, this depends on your NLS_TERRITORY setting.