Calculating sum of a values after join - mysql

Question

I have these tables:
CREATE TABLE `items` (
`itemId` mediumint(8) unsigned NOT NULL AUTO_INCREMENT,
`itemCategoryId` mediumint(8) unsigned DEFAULT NULL,
`name` varchar(255) NOT NULL,
PRIMARY KEY (`itemId`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;
CREATE TABLE `orders` (
`orderId` mediumint(8) unsigned NOT NULL AUTO_INCREMENT,
`customerId` tinyint(3) unsigned NOT NULL,
PRIMARY KEY (`orderId`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;
CREATE TABLE `orders_items` (
`orderItemId` mediumint(8) unsigned NOT NULL AUTO_INCREMENT,
`orderId` mediumint(8) unsigned NOT NULL,
`itemId` mediumint(8) unsigned NOT NULL,
`price` decimal(10,2) unsigned NOT NULL DEFAULT '0.00',
PRIMARY KEY (`orderItemId`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;
CREATE TABLE `order_items_quantity` (
`orderItemId` mediumint(8) unsigned NOT NULL,
`size` tinyint(3) unsigned DEFAULT NULL,
`quantity` smallint(5) unsigned NOT NULL,
UNIQUE KEY `unique` (`orderItemId`,`size`,`quantity`) USING BTREE
) ENGINE=InnoDB DEFAULT CHARSET=utf8;
INSERT INTO `items` (`itemId`, `itemCategoryId`, `name`)
VALUES
(1, 1, 'Jeans Model A (Category Jeans)'),
(2, 1, 'Jeans Model B (Category Jeans)'),
(3, 2, 'T-Shirt Model A (Category T-Shirt)');
INSERT INTO `orders` (`orderId`, `customerId`)
VALUES
(1, 1),
(2, 2),
(3, 1);
INSERT INTO `orders_items` (`orderItemId`, `orderId`, `itemId`)
VALUES
(1, 1, 1),
(2, 1, 2),
(3, 2, 1),
(4, 2, 2),
(5, 3, 1),
(6, 3, 3);
INSERT INTO `order_items_quantity` (`orderItemId`, `size`, `quantity`)
VALUES
(1, 1, 2),
(1, 2, 3),
(2, 1, 3),
(2, 2, 5),
(3, 1, 1),
(3, 2, 2),
(4, 1, 1),
(4, 2, 1),
(5, 1, 4),
(6, 1, 3);
I can't merge 'order_items' with 'order_items_quantity' because I have other fields in the first table about the items regardless the size (es. their prices in that moment) that would be wasted disk space if I repeat them in only one table.
I need a query to get the sum of all the ordered quantities of any item of a certain category by each customer regerdless of the size. Something like:
customerId itemCategoryId total_quantity_ordered
1 1 17
2. 1 5
2. 2. 3
I wrote this query:
SELECT total_quantities.total_quantity_ordered, orders.customerId, items.itemCategoryId FROM orders
JOIN (
SELECT orders_items.orderId, SUM(order_items_quantity.quantity) AS total_quantity_ordered
FROM orders_items
JOIN order_items_quantity ON order_items_quantity.orderItemId=orders_items.orderItemId
GROUP BY orders_items.orderId
) AS total_quantities ON total_quantities.orderId=orders.orderId
JOIN orders_items ON orders_items.orderId=orders.orderId
JOIN items ON items.itemId=orders_items.itemId
GROUP BY orders.customerId, items.itemCategoryId
but it selects only the first order of every customer containing that categoryId. Any help is appreciated.
SQL Fiddle: https://www.db-fiddle.com/f/bnxomXfobBN25nTJvASVdL/0

Answer 1

You don't need the subquery:
SELECT o.customerId, i.itemCategoryId SUM(q.quantity) AS total_quantity_ordered
FROM orders o
INNER JOIN orders_items oi ON oi.orderId=o.orderId
JOIN order_items_quantity q ON oi.orderItemId=q.orderItemId
JOIN items i ON i.itemId=oi.itemId
GROUP BY o.customerId, i.itemCategoryId