Monthly sales in product list query - php

Question

Can anyone help me solve my complicated sql request?
I have an html page with a product list and to every item i want to join loading and sales information for last 4 months.
My desired result is:
Item1 - Month0 (12 in, 0 out), Month-1 (33 in, 36 out)......
Item2 - Month0 (10 in, 30 out), Month-1 (0 in, 66 out)......
My SQL Queries:
Products(simplified) in method "getProducts":
Select item_id, item_name
From Products
Loading
SELECT item_id, CONCAT(YEAR(`load_date`), MONTH(`load_date`)) AS YearMonth,SUM(load_qty) AS total,
FROM loading
GROUP BY YearMonth
WHERE item_id = ?
ORDER BY YearMonth DESC ', array($productId));
Sales
SELECT item_id, CONCAT(YEAR(`load_date`), MONTH(`load_date`)) AS YearMonth,SUM(load_qty) AS total,
FROM sales
GROUP BY YearMonth
WHERE item_id = ?
ORDER BY YearMonth DESC ', array($productId));
Then I got PHP file to call SQL method:
$products = $productManager->getProducts();
$this->data['portalProducts'] = $portalProducts;
And final HTML file with product list:
<?php foreach ($products as $product): ?>
<table>
<tr>
<td><?php echo date("Y - m", strtotime("now"))?></td> //current month
<td>//here goes current month load</td>
<td>//here goes current month sale</td>
</tr>
<tr>
<td><?php echo date("Y - m", strtotime("-1 month"))?></td> //last month
<td>//here goes last month load</td>
<td>//here goes last month sale</td>
</tr>
..............
</table>
Is it possible to combine all of the results from the above queries into one request and then display it as I mentioned in the beginning...
Thanks in advance.

Answer 1

You can combine your SQL queries as follows:
SELECT p.item_id, p.item_name, cal.year_month, COALESCE( q_in.total, 0 ) AS qty_in, COALESCE( q_out.total, 0 ) AS qty_out
FROM Products AS p
INNER JOIN
( SELECT CONCAT(YEAR(NOW()), MONTH(NOW())) AS `year_month`
UNION
SELECT CONCAT(YEAR(NOW() - INTERVAL 1 MONTH), MONTH(NOW() - INTERVAL 1 MONTH)) AS `year_month` ) AS `cal`
ON 1 = 1
LEFT JOIN
( SELECT `item_id`, CONCAT(YEAR(`load_date`), MONTH(`load_date`)) AS `year_month`, SUM(`load_qty`) AS `total`,
FROM loading
WHERE (`load_date` BETWEEN LAST_DAY(NOW() - INTERVAL 2 MONTH) + INTERVAL 1 DAY AND NOW())
GROUP BY `item_id`, YEAR(`load_date`), MONTH(`load_date`)) AS q_in
ON p.item_id = q_in.item_id AND cal.year_month = q_in.year_month
LEFT JOIN
( SELECT item_id, CONCAT(YEAR(`load_date`), MONTH(`load_date`)) AS `year_month`, SUM(`load_qty`) AS `total`,
FROM sales
WHERE (`load_date` BETWEEN LAST_DAY(NOW() - INTERVAL 2 MONTH) + INTERVAL 1 DAY AND NOW())
GROUP BY `item_id`, YEAR(`load_date`), MONTH(`load_date`)) AS q_out
ON p.item_id = q_out.item_id AND cal.year_month = q_out.year_month
ORDER BY p.item_id, p.item_name, q_in.year_month
Output example:
-------------------------------------------------------
| item_id | item_name | year_month | qty_in | qty_out |
-------------------------------------------------------
| 1 | blah | 201604 | 0 | 16 |
-------------------------------------------------------
| 1 | blah | 201605 | 12 | 16 |
-------------------------------------------------------
Explanation:
I have used "Calendar" sub-query to generate a list of months so that your output will always have a row for the current and the previous months even when total quantity for a given month is 0 in and 0 out:
( SELECT CONCAT(YEAR(NOW()), MONTH(NOW())) AS YearMonth
UNION
SELECT CONCAT(YEAR(NOW() - INTERVAL 1 MONTH), MONTH(NOW() - INTERVAL 1 MONTH)) AS YearMonth ) AS Cal
Afterwards I use a left join to join the queries for "loading" and "sales".
I have added a
WHERE (load_date BETWEEN LAST_DAY(NOW() - INTERVAL 2 MONTH) + INTERVAL 1 DAY AND NOW())
to each of the sub-queries to restrict the calculation to current and last month only. This is to improve performance.
Note: I have not tested the query in MySQL