SQL Sum Calculation Confusion - mysql

Question

I am new with mysql and working to change a store application to make it have two stock. I created a table to store stock quantity:
Then I plan to create a view with stock quantity, per store, per SKU. I using the following query:
SELECT
`stockList`.`sku`,
SUM(A.`stockQty`) AS 'store1',
SUM(B.`stockQty`) AS 'store2',
SUM(`stockList`.`stockQty`) AS 'total'
FROM `stockList`
LEFT JOIN (
SELECT * FROM `stockList` WHERE `idStock`=1
) AS A
ON `stockList`.`sku`=A.`sku`
LEFT JOIN (
SELECT * FROM `stockList` WHERE `idStock`=2
) AS B
ON `stockList`.`sku`=B.`sku`
GROUP BY `stockList`.`sku`
Per resulting table, calculation is not proper and I could not identify the logic:
SKU 43 should show for store1 = 9 and for store2 = 10, total = 19. This is what they show if I execute the select queries alone. Please, let me know if I misunderstood how this sum logic works.

Answer 1

You might to use SUM on subquery to calculate Totle price by sku
LEFT JOIN may make some fields not match causing NULL so use IFNULL to preset value 0
You can try this.
SELECT
T.sku,
SUM(T.stockQty) as totle,
IFNULL(A.`store1`,0) AS `store1`,
IFNULL(B.`store2`,0) AS `store2`
FROM `stockList` AS T
LEFT JOIN
(
SELECT sku,SUM(`stockQty`) as `store1`
FROM `stockList`
WHERE `idStock`=1
GROUP BY sku
) as A ON A.sku = T.sku
LEFT JOIN
(
SELECT sku,SUM(`stockQty`) as `store2`
FROM `stockList`
WHERE `idStock`=2
GROUP BY sku
) AS B ON T.sku =B.sku
GROUP BY T.sku
sqlfiddle

Answer 2

Your query is much more complicated than it needs to be. You can just do this:
SELECT
sku,
SUM(stockQty) as total,
SUM(IF(idStock=1,stockQty,0)) AS `store1`,
SUM(IF(idStock=2,stockQty,0)) AS `store2`
FROM `stockList`
GROUP BY sku
Output:
sku total store1 store2
36 10 10 0
37 3 3 0
38 4 4 0
39 3 3 0
40 10 10 0
41 12 12 0
42 12 12 0
43 19 9 10