Update Current Stock levels

Question

Hi i am currenlty having a problem with some pl/sql and wondere if somebody could help me. Im trying to write a trigger so that when a client chooses their product it deducts the amount the client has chosen from the products stock list. Here is what i have so far:
CREATE OR REPLACE TRIGGER "STOCK"
AFTER
insert or update on "ORDERLINE"
begin
update products p set product_stock =
(select sum(p.product_stock - ol.quantity) from products p, orderline ol
where p.product_id = ol.product_id);
end;
currently this seems to be adding high numbers to the stock level for all products and setting them the same i need to have it do the calculation on seperate products
Thanx in advanced Chris

Answer 1

user11967314 wrote:
Ok the trigger works wondefullyNo it does not. It only works "wonderfully" in a single session mode. In multi-session mode it is a recipie for a deadlock. Assume user1 orders product1 and then product2 while user2 orders product2 and then product1. Both users order first item at the same time. So trigger in user1 session updates and therefore locks product1 row in table products while user2 session updates and therefore locks product2 row in table products. Now user1 orders product2 and since user2 has product2 row in table products locked, user1 session waits for that lock to be relased. Meawhile user2 orders product1 and since user1 has product1 row in table products locked he waits for that lock to be relased. Voila, we have a deadlock.
SY.