with data1 as 
(
SELECT
    MONTHLY AS YM
    ,date(MONTHLY,'+1 months') as atoYM
 --   , 算出したMRR AS MRR
    --MRR = 前月のMRR + 前月のNEW_MRR + 前月のEXPANSION_MRR - 前月のDOWNGRADE_MRR - 前月のCHURN_MRR
    ,NEW_MRR + EXPANSION_MRR + DOWNGRADE_MRR + CHURN_MRR AS MRR0
FROM
 MRR_DATA
ORDER BY
MONTHLY

),data2 as
(

SELECT
 A.YM,
 CASE WHEN B.atoYM IS NULL THEN 0 ELSE B.MRR0 END as MRR1
FROM
 data1 as A
LEFT JOIN data1 as B
ON A.YM = B.atoYM
)



SELECT
 A.YM,
 ifNull(A.MRR1,0) + ifNull(B.MRR1,0) AS MRR
FROM data2 as A
left join data2 as B
ON A.YM = date(B.YM,'+1 months')