Store procedure help

Question

is it possible to write store procedure for inserting records and multiplying them
description qt rate Amount
drop procedure a1;
create or replace procedure a1
a_description in varchar2,
a_qt in number,
a_rate in number,
a_amount in number)
as
begin
insert into employee_record values (a_description,a_qt,a_rate,a_qt * a_rate);
end;
is it possible that column amount calculates the amount itself
when i try to execute ( 'Hard Drive', 4, 100)
it gives me an error message .
wrong number or types of arguments in call to 'INSERT_a1'
when i try to run it with ('Hard Drive',4,100, 5) it inserts values and also updates column with correct amount which is 400 .
it would be kind of you if you could show me the a better way to write this store procedure or where i should makes changes.
so that my amount column calculates the total itself
thanks

Answer 1

Hi,
Someoneelse is right: storing columns that depend entirely on other columns is usually a bad idea. Compute the amount in queries, as needed, or create a view that computes amount.
If you really must store it in the table, then you can use a trigger, like this:
CREATE OR REPLACE TRIGGER employee_record_biu
BEFORE INSERT OR UPDATE OF qt, rate, amount
                             ON employee_record
FOR EACH ROW
BEGIN
    :NEW.amount := :NEW.qt * :NEW.rate;
END;
/This will automatically run whenever you issue an INSERT or UPDATE statement that references the columns involved. If that statement provides a value for amount, that value will be ignored. Amount will always be calculated from qt and rate.
Starting in Oracel 11, you can create a virtual column, which will probably be better than a trigger.
http://download.oracle.com/docs/cd/B28359_01/server.111/b28286/statements_7002.htm#sthref7273