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