with tmp(YM,pre_YM) as(
values('2022-01-01',null),
      ('2022-02-01','2022-01-01'),
      ('2022-03-01','2022-02-01'),
      ('2022-04-01','2022-03-01'),
      ('2022-05-01','2022-04-01'),
      ('2022-06-01','2022-05-01'),
      ('2022-07-01','2022-06-01'),
      ('2022-08-01','2022-07-01'),
      ('2022-09-01','2022-08-01'),
      ('2022-10-01','2022-09-01'),
      ('2022-11-01','2022-10-01'),
      ('2022-12-01','2022-11-01')
      ),

    mrr_temp as (
    select t.YM,
        m.NEW_MRR + m.EXPANSION_MRR - m.DOWNGRADE_MRR - m.CHURN_MRR mrr
    from tmp t
    left join MRR_DATA m
    on t.pre_YM = m.MONTHLY
    ),

    mrr_base as (
    select t.YM YM,
            case when m1.mrr is null then 0 else m1.mrr end last_mrr,
            case when m2.mrr is null then 0 else m2.mrr end current_mrr
    from tmp t
    left join mrr_temp m1
    on t.pre_YM = m1.YM
    left join mrr_temp m2
    on t.YM = m2.YM
    )

select YM,
        last_mrr + current_mrr MRR
from mrr_base
order by 1
;