Ordering issue when using SQL variable - mysql

Question

I run this query:
SELECT stockcarddetail.id, stockcarddetail.date, stockcarddetail.quantity, stockcarddetail.pricePerItem
FROM Stockcard
LEFT JOIN staff
ON staff.branchId = stockcard.branchId
LEFT JOIN stockcarddetail
ON stockcarddetail.stockcardId = stockcard.id
WHERE staff.username = 'jemmy.h'
AND stockcarddetail.quantity > 0
AND stockcard.productId = '98924a5f-6afb-11e7-8dd4-2c56dcbcb038'
ORDER BY date ASC
and get the result below:
id | date | quantity| pricePerItem
50 | 2017-10-15 | 10.00 | 10000.00
1 | 2017-10-18 | 20.00 | 10000.00
Then, I need to calculate the cumulative of quantity based on the order above, so I run this query:
SELECT a.*, #tot:=#tot + a.quantity FROM
(SELECT #tot:= 0)b
JOIN
(SELECT stockcarddetail.id, stockcarddetail.date, stockcarddetail.quantity, stockcarddetail.pricePerItem
FROM Stockcard
LEFT JOIN staff
ON staff.branchId = stockcard.branchId
LEFT JOIN stockcarddetail
ON stockcarddetail.stockcardId = stockcard.id
WHERE staff.username = 'jemmy.h'
AND stockcarddetail.quantity > 0
AND stockcard.productId = '98924a5f-6afb-11e7-8dd4-2c56dcbcb038'
ORDER BY date ASC) a
Then I got this result:
id | date | quantity| pricePerItem | #tot
1 | 2017-10-18 | 20.00 | 10000.00 | 20
50 | 2017-10-15 | 10.00 | 10000.00 | 30
However, the result that I want is like this:
id | date | quantity| pricePerItem | #tot
50 | 2017-10-15 | 10.00 | 10000.00 | 10
1 | 2017-10-18 | 20.00 | 10000.00 | 30
How can I get the expected result?
EDIT
Simplified version of the problem can be found here: http://sqlfiddle.com/#!9/f6ad91/3

Answer 1

From what I understand from you, you want the cumulative total for each entry.
I suggest ditching the variable and relying on a subquery instead:
SELECT
scd.id,
scd.date,
scd.quantity,
scd.pricePerItem,
(SELECT SUM(scd1.quantity) FROM StockcardDetail AS scd1 WHERE scd1.stockcardId = scd.stockcardId AND scd1.date <= scd.date) AS total
FROM Stockcard
LEFT JOIN staff ON staff.branchId = stockcard.branchId
LEFT JOIN stockcarddetail AS scd ON scd.stockcardId = stockcard.id
WHERE staff.username = 'jemmy.h'
AND scd.quantity > 0
AND stockcard.productId = '98924a5f-6afb-11e7-8dd4-2c56dcbcb038'
ORDER BY scd.date ASC
The idea behind this is to make it select the sum of all entries prior (including the current one) for each entry.

Answer 2

As per my understanding, you should get the expected output from your query. But, you aren't getting your expected output, then other possible solution is (WITHOUT JOIN)
SET #tot:= 0;
SELECT
stockcarddetail.id,
stockcarddetail.date,
stockcarddetail.quantity,
stockcarddetail.pricePerItem,
#tot:=#tot + stockcarddetail.quantity as Total
FROM Stockcard
LEFT JOIN staff ON staff.branchId = stockcard.branchId
LEFT JOIN stockcarddetail ON stockcarddetail.stockcardId = stockcard.id
WHERE staff.username = 'jemmy.h' AND stockcarddetail.quantity > 0 AND stockcard.productId = '98924a5f-6afb-11e7-8dd4-2c56dcbcb038'
ORDER BY date ASC