Creating function to calculate average value

Question

Hi,
The below query was successfully return an average value. It returned 1 row.
SELECT AVG(Volume)
FROM security
WHERE
Type = 'Future' AND
Rating = 'AAA' AND
Code = 1 AND
(Day = ''14-mar-09' OR
Day = '16-mar-09' OR
Day = '');
I tried to use that function on my created function below.
CREATE OR REPLACE FUNCTION fn_Vol_Average
( v_DayLast_1_Week IN DATE,
v_DayLast_2_Week IN DATE,
v_DayLast_3_Week IN DATE )
RETURN NUMBER IS
v_Vol_Average NUMBER;
BEGIN
SELECT AVG(Volume) INTO v_Vol_Average
FROM security
WHERE
Type = 'Future' AND
Rating = 'AAA' AND
Code = 1 AND
(Day = v_DayLast_1_Week OR
Day = v_DayLast_2_Week OR
Day = v_DayLast_3_Week);
RETURN NVL(v_Vol_Average, NULL);
END;
I called that function by the following query. it was work, however it return the whole rows. It looks like the function perform the average calculation of each rows on the table.
Can anyone help me what is going on with the logic?
select fn_Vol_average('14-mar-09','16-mar-09','')
from security
--

Answer 1

But since your function calculates the average over the whole security table, you wouldn't call this from a select statement which also reads the security table.
You just want to execute it once.
declare
   l_vol_average number;
begin
   l_vol_average := fn_Vol_average('14-mar-09','16-mar-09','');
   dbms_output.put_line(l_vol_average);
end;By the way, be careful with your date parameters. You should use TO_DATE with a proper format mask to prevent conversion errors.