select 
    MONTHLY,
    sum(MRR) OVER (ORDER BY MONTHLY rows between unbounded preceding and current row) as MRR
from (
select 
    MONTHLY,
    coalesce(LAG(NEW_MRR) OVER(order by MONTHLY),0)
      + coalesce(LAG(EXPANSION_MRR) OVER(order by MONTHLY),0)
      - coalesce(LAG(DOWNGRADE_MRR) OVER(order by MONTHLY),0)
      - coalesce(LAG(CHURN_MRR) OVER(order by MONTHLY),0) as MRR
from MRR_DATA
)
order by 1