Rolling sum for a column in mysql - mysql

Question

I would like to get the rolling sum for the growth column for the following sample data which can be found here dbfiddle
The output should look like,
Growth RollingSum TMonth TYear
511 511 AUG 2019
79 590 SEP 2019
-6 584 OCT 2019
0 584 NOV 2019
-4 580 DEC 2019
45 625 JAN 2020
-1 624 FEB 2020
7 631 MAR 2020
-22 609 APR 2020
-6 603 MAY 2020
-20 583 JUN 2020
0 583 JUL 2020
My attempt is as follows. I am only getting the total for values in the Growth column
SELECT r1.Growth, sum(r2.Growth) AS rolling_total ,r1.Month,r1.Year
FROM Report AS r1 JOIN Report AS r2
ON r1.Month = r1.Month
GROUP BY r1.Month;
The above gives me the result as,
Growth RollingSum TMonth TYear
511 583 AUG 2019
79 583 SEP 2019
-6 583 OCT 2019
0 583 NOV 2019
-4 583 DEC 2019
45 583 JAN 2020
-1 583 FEB 2020
7 583 MAR 2020
-22 583 APR 2020
-6 583 MAY 2020
-20 583 JUN 2020
0 583 JUL 2020
I want to avoid using procedures,cursors or functions if at all possible. I am using mysql 8.0.17

Answer 1

You can use SUM() window function but with the correct ordering.
This ordering:
ORDER BY DATE_FORMAT(`TMonth`, '%M'), `TYear`
is wrong because DATE_FORMAT() with these parameters returns NULL, so you simply sort by Year.
See the demo.
It is coincidental that you get correct results.
The correct ordering is:
ORDER BY STR_TO_DATE(CONCAT(TYear, TMonth, '01'), '%Y%b%d')
So use this:
SELECT
Growth,
SUM(Growth) OVER (ORDER BY STR_TO_DATE(CONCAT(TYear, TMonth, '01'), '%Y%b%d')) RollingSum,
TMonth,
TYear
FROM Report
See the demo.
Results:
> Growth | RollingSum | TMonth | TYear
> -----: | ---------: | :----- | ----:
> 511 | 511 | AUG | 2019
> 79 | 590 | SEP | 2019
> -6 | 584 | OCT | 2019
> 0 | 584 | NOV | 2019
> -4 | 580 | DEC | 2019
> 45 | 625 | JAN | 2020
> -1 | 624 | FEB | 2020
> 7 | 631 | MAR | 2020
> -22 | 609 | APR | 2020
> -6 | 603 | MAY | 2020
> -20 | 583 | JUN | 2020
> 0 | 583 | JUL | 2020

Answer 2

Since you are using mysql 8 use window functionn SUM
DATE_FOMAT are not working, so you need STR_TO_DATE
CREATE TABLE roll_month (
`Growth` INTEGER,
`RollingSum` INTEGER,
`TMonth` VARCHAR(3),
`TYear` INTEGER
);
INSERT INTO roll_month
(`Growth`, `RollingSum`, `TMonth`, `TYear`)
VALUES
('511', '511', 'AUG', '2019'),
('79', '590', 'SEP', '2019'),
('-6', '584', 'OCT', '2019'),
('0', '584', 'NOV', '2019'),
('-4', '580', 'DEC', '2019'),
('45', '625', 'JAN', '2020'),
('-1', '624', 'FEB', '2020'),
('7', '631', 'MAR', '2020'),
('-22', '609', 'APR', '2020'),
('-6', '603', 'MAY', '2020'),
('-20', '583', 'JUN', '2020'),
('0', '583', 'JUL', '2020');
SELECT
`Growth`
, SUM(`Growth`) OVER( ORDER BY STR_TO_DATE(CONCAT('01-',`TMonth`,'-',`TYear`), '%d-%M-%Y') ROWS UNBOUNDED PRECEDING) RollingSum
, `TMonth`, `TYear`
FROM roll_month
Growth | RollingSum | TMonth | TYear
-----: | ---------: | :----- | ----:
511 | 511 | AUG | 2019
79 | 590 | SEP | 2019
-6 | 584 | OCT | 2019
0 | 584 | NOV | 2019
-4 | 580 | DEC | 2019
45 | 625 | JAN | 2020
-1 | 624 | FEB | 2020
7 | 631 | MAR | 2020
-22 | 609 | APR | 2020
-6 | 603 | MAY | 2020
-20 | 583 | JUN | 2020
0 | 583 | JUL | 2020
db<>fiddle here

Answer 3

With the values and names that i took from your table, this cross join would give you the output you want way more easy:
select r1.Growth, r1.TMonth, TYear,
(#s := #s + r1.Growth) as RollingSum
from Report r1 cross join
(select #s := 0) p;