Help needed - driving me nuts

i have a database made in oracle. I need to make a query that will take the price of a book, and the ISBN of a book. Find out how many of the same ISBN is in the database and calculates the price.

The only thing is that when i run my query.....it takes all the the ISBNs in the database, no matter if the ISBN is specified, it just takes the lot. Could someone have a lok at this query and see if there is anything obviously wrong.

Thanks in advance
Cokes

Don't make your function's argument name identical to your table column name, make the following changes:

CREATE OR REPLACE FUNCTION calculate_total_revenue
(P_ISBN IN book.ISBN%TYPE,
P_PRICE IN book.PRICE%TYPE)
RETURN number IS

total_revenue number;
number_of_sales number;

BEGIN
SELECT count(ISBN)
INTO number_of_sales
FROM purchases
WHERE purchases.ISBN = P_ISBN;

total_revenue:= (P_PRICE * number_of_sales);
return (total_revenue);
END;

Thanks a lot buddy.......i'm useless with all this oracle stuff. Just another thing i gotta do for uni.

Thank you