Calculating Cumulative values using MySQL - mysql

Question

I have this table:
Month_Year MV MI
----------------------------------------------------------
August 2016 3 100
October 2016 2 150
September 2016 1 100
January 2017 4 200
I need to create the next output table
Month_Year MV AMV MI AMI
----------------------------------------------------------
January 2016 0 0 0 0
...
July 2016 0 0 0 0
August 2016 3 3 100 100
September 2016 1 4 100 200
October 2016 2 6 150 350
November 2016 0 6 0 350
December 2016 0 6 0 350
January 2017 4 10 200 550
At month M, for column AMV, AMV is the ccumulative value of all the AV ones before that month and month M. For example, AMV is 4 on 'September 2016' because in 'August 16' AV is 3 and 1 for 'September 2016'. Similarly for AMI. How can this be done?. Notice that the Month_Year column is not necessarily ordered. Thanks
ADDITIONAL INFO
After using the DATE_FORMAT(original_Date, '%Y %m') I was able to convert the first table to:
Month_Year MV MI
----------------------------------------------------------
2016 08 3 100
2016 10 2 150
2016 09 1 100
2017 01 4 200
Could this simplify the problem? Why not to use DATE_FORMAT(original_Date, '%m %Y')?

Answer 1

The month-year format is a big big NO, and you have to somehow overcome it. For this example I create a MEMORY table months, and I use several joins with this table.
create table months (month_year_int int, month_year varchar(30)) engine=memory;
insert months
select 201601 as month_year_int, 'January 2016' as month_year
union all select 201602, 'February 2016'
union all select 201603, 'March 2016'
union all select 201604, 'April 2016'
union all select 201605, 'May 2016'
union all select 201606, 'June 2016'
union all select 201607, 'July 2016'
union all select 201608, 'August 2016'
union all select 201609, 'September 2016'
union all select 201610, 'October 2016'
union all select 201611, 'November 2016'
union all select 201612, 'December 2016'
union all select 201701, 'January 2017'
;
All these would have been avoided if you had used a proper model for your data. Anyway, this is a solution whis does not use the My-Sql proprietary variable pattern (a rextester demo here):
select
x.month_year,
coalesce(t.mv, 0) MV,
sum(y.mv) as AMV,
coalesce(t.mi, 0) AMV,
sum(y.mi) as AMI from
(
select
m.month_year_int,
m.month_year,
coalesce(t.mv, 0) as mv,
coalesce(t.mi) as mi
from months m left join test t on m.month_year = t.month_year
) x
left join
(
select
m.month_year_int,
m.month_year,
coalesce(t.mv, 0) as mv,
coalesce(t.mi) as mi
from months m
left join test t on m.month_year = t.month_year
) y on x.month_year_int > y.month_year_int - 1
left join test t on x.month_year = t.month_year
group by x.month_year_int
order by x.month_year_int
;