Select Sum from two joined tables

Question

There are structures:

CREATE TABLE `invoices` (
`id` int(10) unsigned NOT NULL AUTO_INCREMENT,
`date` date NOT NULL,
PRIMARY KEY (`id`)
) ENGINE=InnoDB;

INSERT INTO `invoices` VALUES (1,'2018-09-22');

CREATE TABLE `products` (
`id` int(10) unsigned NOT NULL AUTO_INCREMENT,
`invoice_id` int(10) unsigned NOT NULL,
`amount` decimal(10,2) unsigned NOT NULL,
`quantity` smallint(5) unsigned NOT NULL,
PRIMARY KEY (`id`)
) ENGINE=InnoDB;

INSERT INTO `products` VALUES (1,1,150.00,2),(2,1,60.00,3),(3,1,50.00,1);

CREATE TABLE `payments` (
`id` int(10) unsigned NOT NULL AUTO_INCREMENT,
`invoice_id` int(10) unsigned NOT NULL,
`amount` decimal(10,2) unsigned NOT NULL,
`date` date NOT NULL,
PRIMARY KEY (`id`)
) ENGINE=InnoDB;

INSERT INTO `payments` VALUES (1,1,400.00,'2018-09-23'),(2,1,80.00,'2018-09-23');

I have this query:

select i.id, sum(pr.amount * pr.quantity) as productAmount, 
sum(pm.amount) as paymentAmount
from invoices as i
left join products as pr on pr.invoice_id=i.id
left join payments as pm on pm.invoice_id=i.id
group by i.id

and have this result:

+----+---------------+---------------+
| id | productAmount | paymentAmount |
+----+---------------+---------------+
|  1 |       1060.00 |       1440.00 |
+----+---------------+---------------+
1 row in set (0,00 sec)

However, I want to get the following result:

+----+---------------+---------------+
| id | productAmount | paymentAmount |
+----+---------------+---------------+
|  1 |        530.00 |        480.00 |
+----+---------------+---------------+
1 row in set (0,00 sec)

I want sum amount of products and sum amount of payments grouped by invoice.id.
What should be the query in this case?

Answer 1

By the addition join on payments, of which there are two, the productAmount got doubled:

select i.id, sum(distinct pr.amount * pr.quantity) as productAmount, 
sum(distinct pm.amount) as paymentAmount
from invoices as i
join products as pr on pr.invoice_id=i.id
join payments as pm on pm.invoice_id=i.id
group by i.id;

Also replaced LEFT JOIN with JOIN as you don't care about non-matching entries.

Answer 2

Here is another option:

SELECT ProductAmt.id
    ,productAmount
    ,paymentamt.paymentamount
FROM (
    SELECT i.id
        ,sum(pr.amount * pr.quantity) AS productAmount
    FROM invoices AS i
    LEFT JOIN products AS pr ON pr.invoice_id = i.id
    GROUP BY i.id
    ) ProductAmt
LEFT JOIN (
    SELECT i.id
        ,sum(pm.amount) AS paymentAmount
    FROM invoices AS i
    LEFT JOIN payments AS pm ON pm.invoice_id = i.id
    GROUP BY i.id
    ) PaymentAmt ON productAmt.id = paymentamt.id

SQL Fiddle example here