MySQL - Calculation of invoice balance grouped by client using 3 tables - mysql

Question

I'm currently working on a small client management system and I came accross a feature I can't yet get to work in pure SQL (currently using PHP foreach with lot of lazy loading, so very slow).
I am trying to get the current balance of each clients, so getting the sold of each invoice (by substracting SUM of payments) payment and SUM them. Each clients has invoices in the systems and each invoices can have multiple payments.
Here's my simplified tables for the purpose of being generic:
[Clients]
- id
- name
[Invoices]
- id
- client_id
- amount
[Payments]
- id
- invoice_id
- amount (positive number)
So basically, I want to get this:
+--------------------+----------------------+
| name | balance |
+--------------------+----------------------+
| Client 1 | 342,46 |
| Client 2 | 0,00 |
+--------------------+----------------------+
To get the invoice sold, I need SUM(invoices.amount) - SUM(payments.amount)) but my query isn't working at all. Here's what I got so far:
SELECT DISTINCT
c.name,
SUM(x.sold) AS balance
FROM
clients AS c
RIGHT JOIN
(
SELECT SUM(i.invoiceAmount - total_payments) AS sold
FROM invoices
WHERE i.client_id = c.id
RIGHT JOIN (
SELECT p.id, p.invoice_id, SUM(p.transactionAmount) AS total_payments
FROM payments AS p
GROUP BY p.invoice_id
) AS p ON p.invoice_id=i.id
GROUP BY i.client_id
) AS x ON x.client_id=c.id
GROUP BY c.name
ORDER BY c.name ASC
Does anybody ever done this before? I never did and it's pretty tricky.
Note: I tried to be as much generic as possible, so it may help other people in a similar situation.
UPDATE:
Using #GordonLinoff answer, I was able to get what I wanted using the query he provided me.
select name, SUM(invoices - IFNULL(payments, 0)) as balance
from (
select name, sum(amount) as invoices, sum(payments) as payments
from (select c.id, c.name, i.id as invoiceid, i.amount, sum(p.amount) as payments
from clients c left join
invoices i
on c.id = i.client_id left join
payments p
on p.invoice_id = i.id
group by c.id, c.name, invoiceid, i.amount
) ci
group by name
) x
The result is exactly as I expected.

Answer 1

Aggregating through hierarchical structures is tricky. Here is one method that joins the tables together and then uses two levels of aggregation:
select name, sum(amount) as invoices, sum(payments) as payments
from (select c.id, c.name, i.id, i.amount, sum(p.amount) as payments
from clients c left join
invoices i
on c.id = i.client_id left join
payments p
on p.invoice_id = i.id
group by c.id, c.name, i.id, i.amount
) ci
group by name;