Question

I have two db tables Fine and Fine_payment.
Fine has fields
* fine_id[pk]
* fine_amount.

Fine_payment has fields
* fine_payment_id[pk]
* fine_id
* payment_amount

So every Fine can have multiple payments. How would I go about selecting those Fines that haven’t been paid fully and show the unpaid amount?

Oracle DB.

Answer 1

select fine_id, fine_amount
---------------------------------------------------------------
-- add a coalesce here, in case "payments" returns a NULL match
---------------------------------------------------------------
, (fine_amount - coalesce(payments.already_paid, 0)) as outstanding_amount
from Fine left outer join
(
  select fine_id
  , sum(coalesce(payment_amount, 0)) as already_paid
  from Fine_payment
  group by fine_id
) payments
on Fine.fine_id = payments.fine_id
where Fine.fine_amount <> coalesce(payments.already_paid, 0)

EDIT: inner join replaced with left outer join