How to write queries to calculate today's due amount? - mysql

Question

I have scheduled payments, so I have these tables:
customer
+id
paymentSchedule
+id
+customer_id
+amount //total price
+dueDate //date to be paid
payments
+id
+date
+customer_id
+paymentSchedule_id
+amount //amount paid, it can be a partial payment
How do I write a query to get Today's due amount by customer.
I mean I need to join the tables (thats my main problem) and then substract the
sum of the payments.mount minus the sum of the scheduledPaymens.amount
but.. how?
Thanks in advance

Answer 1

This is probably not 100%, but should be pretty solid to help you tweak:
SELECT customer_id, (due.amount - paid.amount) as amountDue
FROM
(SELECT customer_id, SUM(amount) as amount
FROM paymentSchedule
WHERE dateDate <= getDate()
and customer_id = #custid) as due
LEFT JOIN
(SELECT customer_id, SUM(amount) as amount
FROM payments
WHERE customer_id = #custid) as paid ON paid.customer_id = due.customer_id

Answer 2

Ok, this is how I understood the problem. I simplified the tables because they where just complicating things, and adding dates is just straight forward.
PaymentSchedule
+----+-------------+-----------------+
| id | customer_id | original_amount |
+----+-------------+-----------------+
| 1 | Tom | 100 |
| 2 | Tom | 200 |
| 3 | Tom | 300 |
| 4 | Moe | 400 |
+----+-------------+-----------------+
Payments
+----+--------------------+-------------+
| id | paymentSchedule_id | paid_amount |
+----+--------------------+-------------+
| 1 | 1 | 70 |
| 2 | 2 | 150 |
| 3 | 2 | 50 |
| 4 | 4 | 300 |
| 5 | 4 | 25 |
+----+--------------------+-------------+
Result of query
+-------------+-------------------+-----------------+-----------+----------------+
| CUSTOMER_ID | PAYMENTSCHEDULEID | ORIGINAL_AMOUNT | TOTALPAID | PENDINGPAYMENT |
+-------------+-------------------+-----------------+-----------+----------------+
| Tom | 1 | 100 | 70 | 30 |
| Tom | 2 | 200 | 200 | 0 |
| Tom | 3 | 300 | 0 | 300 |
| Moe | 4 | 400 | 325 | 75 |
+-------------+-------------------+-----------------+-----------+----------------+
Query with double select
select *, s.original_amount - s.TotalPaid as PendingPayment from (
select
ps.customer_id, ps.id as PaymentScheduleId, ps.original_amount,
coalesce(sum(p.paid_amount), 0) as TotalPaid
from paymentSchedule ps
left join payments p on p.paymentSchedule_id = ps.id
group by ps.customer_id, PaymentScheduleId, ps.original_amount
) as S
Query with single select
select
ps.customer_id, ps.id as PaymentScheduleId, ps.original_amount,
coalesce(sum(p.paid_amount), 0) as TotalPaid,
ps.original_amount - coalesce(sum(p.paid_amount), 0) as PendingPayment
from paymentSchedule ps
left join payments p on p.paymentSchedule_id = ps.id
group by ps.customer_id, PaymentScheduleId, ps.original_amount
The result of both queries is the same. I just wonder which one runs faster. You can try both and tell us :)
Let me know if this this is the result you expected

Answer 3

Something like this should be a good starting point for you to tweak.
SELECT c.*
FROM customer c
INNER JOIN paymentSchedule ps
ON c.id = ps.customer_id
LEFT JOIN payments p
ON ps.id = p.paymentSchedule_id
WHERE ps.dueDate = 'This depends on how you store dueDate'
AND ps.amount - p.amount > 0