How to sum daily resetting data using MySQL - mysql

Question

I am attempting to plot data cumulatively from a MySQL table which logs a value, resetting to 0 every day. After selecting the values using select * from table where DateTime BETWEEN DateA AND DateB, the data looks like this: current data. I would like the output to look like this: preferred data, ignoring the daily resets.
As I am a novice in SQL I was unable to find a solution to this. I did, however, obtain the correct output in Matlab using a for loop:
output = data;
for k=1:(size(data, 1)-1)
% check if next value is smaller than current
if data(k+1)<data(k)
% add current value to all subsequent values
output = output + (1:size(data, 1)>k)'.*input(k);
end
end
I would like the final product to connect to a web page, so I am curious if it would be possible obtain a similar result using only SQL. While I have tried using SUM(), I have only been able to sum all values, but I need to add the last value each day to all subsequent values.

Answer 1

Using CTE and comparing dates, you can sum all values each date.
Let's say that table1 below is defined.
create table table1 (col_date date, col_value int);
insert into table1 values
('2020-07-15',1000),
('2020-07-15',2000),
('2020-07-16',1000),
('2020-07-16',3000),
('2020-07-16',4000),
('2020-07-17',1000),
('2020-07-18',2000),
('2020-07-19',1000),
('2020-07-19',1000),
('2020-07-19',2000),
('2020-07-19',3000),
('2020-07-20',4000),
('2020-07-20',5000),
('2020-07-21',6000)
;
In this case, the query looks like this:
with cte1 as (
select col_date, sum(col_value) as col_sum from table1
where col_date between '2020-07-16' and '2020-07-20'
group by col_date
)
select a.col_date, max(a.col_sum), sum(b.col_sum)
from cte1 a inner join cte1 b on a.col_date >= b.col_date
group by a.col_date;
The output is below:
col_date |max(a.col_sum) |sum(b.col_sum)
2020-07-16 |8000 | 8000
2020-07-17 |1000 | 9000
2020-07-18 |2000 |11000
2020-07-19 |7000 |18000
2020-07-20 |9000 |27000
The column of max() is just for reference.