select quantity into quantity1 from zakaz;

insert into zakaz (kod_tovar,kod_zaka,quantity) values(11,2,5)

create or replace 
trigger trig4 after update of quantity   on  orders for each row
declare
quantity1 VARCHAR(25); 
begin
select quantity into quantity1 from products where prod_id = :new.prod_id;
update products set quantity = quantity - quantity1  where prod_id = :new.prod_id;
end trig4;

select * from products;

insert into orders values(1,1,3,150)

select * from products;