I have a query that returns items a person has paid for, the price of that item and the balance. My problem is there are situations where a person may make 2 payments for one item (make a payment, and another payment of the balance later). So the returned table looks like this:
name | invoice_id| inv_date | item_id|item | pay_id | price | paid | balance |
---------|-----------|----------|--------|---------|--------|-------|------|---------|
John Doe| 581 | 2018-4-10| 10 |Transport| 1165 | 8100 | 5400 | 2700 |
John Doe| 581 | 2018-4-10| 10 |Transport| 1030 | 8100 | 2700 | 5400 |
John Doe| 581 | 2018-4-10| 25 |Insurance| 1165 | 24000 | 12000| 12000 |
John Doe| 581 | 2018-4-10| 25 |Insurance| 1030 | 24000 | 12000| 12000 |
---------|-----------|----------|--------|---------| -------|-------|------|---------|
As you can see from the return results, the balance for each second payment is incorrect. Take the second payment of transport for instance, there's a previous payment of 5400 and the current payment is 2700 so (5400 + 2700 = 8100 ) so the balance should be 0. So my question is how can I return the proper balance for each subsequent payment of each item?
Currently I'm returning the balance as (price - paid) but for subsequent payments the balance is incorrect.
you want a window function.
price -
sum(paid) over (partition by item_id order by pay_id desc)
as balance.
you probably want a different order by, use whatever ordering your report uses.