with tmp as(
select MONTHLY as YM,
NEW_MRR,EXPANSION_MRR,DOWNGRADE_MRR,CHURN_MRR
  from MRR_DATA
union
select date(max(MONTHLY),'+1 months'),
0,0,0,0
  from MRR_DATA)
select YM,
case when YM = min(YM) over()
     then 0
     else 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) end as MRR
  from tmp
order by YM;