with diff as (
    select monthly, coalesce(new_mrr, 0) + coalesce(expansion_mrr, 0) - coalesce(downgrade_mrr, 0) - coalesce(churn_mrr, 0) as value
    from mrr_data
    union all
    select date(max(monthly), '+1 month'), null
    from mrr_data
)
select diff.monthly as YM, coalesce(sum(diff2.value), 0) as MRR
from diff
left join diff as diff2
on diff.monthly > diff2.monthly
group by diff.monthly
order by diff.monthly asc