with MRR_DATE_WITH_ID as(
select ROWID as idx,*,
NEW_MRR + EXPANSION_MRR - DOWNGRADE_MRR  - CHURN_MRR
as next_MRR  from MRR_DATA
),
plused_MRR as(
select *, 
case
when idx == 1 then next_MRR
else SUM(next_MRR) OVER (ORDER BY idx)
end
as calculated_MRR
from MRR_DATE_WITH_ID)
select
MONTHLY as YM,
case
when idx == 1 then 0
else LAG(calculated_MRR) OVER (ORDER BY idx)
end as MRR
from plused_MRR

UNION ALL

select date(MAX(MONTHLY), '+1 month')as YM,
(SELECT calculated_MRR FROM plused_MRR WHERE idx = (SELECT MAX(idx) FROM plused_MRR)) as MRR
from plused_MRR