with a as(
select
MONTHLY as YM,
NEW_MRR,
EXPANSION_MRR,
DOWNGRADE_MRR,
CHURN_MRR
from  MRR_DATA
union 
select 
date(max(MONTHLY), '+1 month'),
0,
0,
0,
0
from  MRR_DATA
)
select
YM,
ifnull(
sum(NEW_MRR) over (order by YM rows between unbounded preceding and 1 preceding)  
+ sum(EXPANSION_MRR) over (order by YM rows between unbounded preceding and 1 preceding)
- sum(DOWNGRADE_MRR) over (order by YM rows between unbounded preceding and 1 preceding)
- sum(CHURN_MRR) over (order by YM rows between unbounded preceding and 1 preceding),
    0) as MRR
from a
order by YM