SQL invoice three tables into one query - mysql

Question

Hello,
I have 3 tables:
CREATE TABLE `invoice` (
`id` int(11) NOT NULL,
PRIMARY KEY (id)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4;
INSERT INTO `invoice` (`id`) VALUES
(1),
(2),
(3);
CREATE TABLE `invoice_deduction` (
`id` int(11) NOT NULL,
`invoiceId` int(11) NOT NULL,
`deductionId` int(11) NOT NULL,
PRIMARY KEY (id),
FOREIGN KEY (`invoiceId`) REFERENCES `invoice` (`id`),
FOREIGN KEY (`deductionId`) REFERENCES `invoice` (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4;
INSERT INTO `invoice_deduction` (`id`, `invoiceId`, `deductionId`) VALUES
(1, 2, 1),
(2, 3, 1),
(3, 3, 2);
CREATE TABLE `invoice_item` (
`id` int(11) NOT NULL,
`invoiceId` int(11) NOT NULL,
PRIMARY KEY (id),
FOREIGN KEY (`invoiceId`) REFERENCES `invoice` (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4;
INSERT INTO `invoice_item` (`id`, `invoiceId`) VALUES
(1, 1),
(2, 1),
(3, 1),
(4, 2),
(5, 2),
(6, 3),
(7, 3),
(8, 3);
For example:
The first invoice contains 3 items (total: 3 items)
The second invoice contains 3 items from first invoice (deduction) and 2 new items (total: 5 items)
The third invoice contains 3 items from first invoice (deduction), 2 items from second invoice (deduction) and 3 new items (total: 8 items)
So I want to have a query with this result:
id | count of items (with deductions)
3 | 8
2 | 5
1 | 3
I start with this query:
SELECT
i.id, COUNT(*) as countItems
FROM
invoice i JOIN invoice_item it ON i.id = it.invoiceId
GROUP BY
it.invoiceId
ORDER BY
countItems
DESC
I thank you in advance for your help.

Answer 1

I think you want a cumulative sum:
SELECT i.id, COUNT(*) as countItems,
SUM(COUNT(*)) OVER (ORDER BY it.id)
FROM invoice i JOIN
invoice_item it
ON i.id = it.invoiceId
GROUP BY i.id
ORDER BY countItems;
I have no idea why you are using a LEFT JOIN. I don't know why you would have invoiceId values that do not match a valid invoice. So I switched it to an inner join.