Assistance with a trigger.

Question

I was wondering if someone could help me with this trigger. I get an error when I complete it and I would like it to work.
Here is the code I put in and the corresponding errors:
SQL> create trigger trg_updatecustbalance
2 after insert or update of inv_amount on invoice
3 begin
4 update cust_balance on customer
5 set cust_balance=(cust_balance+invoice.inv_amount)
6 where customer.cust_num=invoice_cust.num;
7 end;
8 /
Warning: Trigger created with compilation errors.
SQL> show errors
Errors for TRIGGER TRG_UPDATECUSTBALANCE:
LINE/COL ERROR
2/1 PL/SQL: SQL Statement ignored
2/21 PL/SQL: ORA-00971: missing SET keyword
SQL>
If I try to update a record I get the following:
SQL> insert into invoice
2 values('8005','1001','27-apr-04','225.40');
insert into invoice
ERROR at line 1:
ORA-04098: trigger 'MILLER6C.TRG_UPDATECUSTBALANCE' is invalid and failed
re-validation
Any assistance would be appreciated. Thanks.
Justin

Answer 1

1) The syntax of an UPDATE statement is
UPDATE <<table name>>
   SET <<column name>>
   ...I assume that CUST_BALANCE is a column in the CUSTOMER table, so the "CUST_BALANCE ON" in your SQL statement is incorrect.
2) In order to refer to elements in the row you just inserted, you need to refer to :new.column_name, not invoice.column_name
3) I'm not sure what INVOICE_CUST.NUM is supposed to be referring to. I'll guess that you mean to refer to the CUST_NUM column in the INVOICE row you just inserted.
4) Assuming you intend this to fire for each row you insert, you need the FOR EACH ROW clause
If all these assumptions are correct, something like this should work
create trigger trg_updatecustbalance
  after insert or update on invoice
  for each row
begin
  update customer
     set cust_balance=(cust_balance+:new.inv_amount)
   where customer.cust_num=:new.cust_num;
end;Is this a homework assignment? Or is it for a real system? If this is for a real system, there are various race conditions and functional problems with this sort of implementation that you need to be aware of. It is generally preferable to use a materialized view to store aggregate information rather than trying to maintain a customer's balance with a trigger.
Justin