Look at UPDATE, INSERT and DELETE triggers. The UPDATE trigger you will need to verify that the quantity and amount have changed and then use the OLD value and subtract from the total and add the NEW value to the total. For DELETE subtract the OLD value from the total and INSERT add NEW value to the total.
If you still have problems post your trigger and we can help investigate further.
Hi thanks for the help , i am just new learner if i make mistake please correct it as i am trying whole heartedly to learn triggers
for this I want to write rule/ trigger which update total cost when we make change to quantity
So following is trigger that I am trying on logical basis, please see
CREATE OR REPLACE TRIGGER UPDATE_TRIGG
AFTER UPDATE OF QUANTITY
FOR EACH ROW
INSERT INTO ORDER
: old.custno ,
Please correct if something got wrong in query as I am very new learner !!