l1

-- Assuming [ACCOUNT_MPL.SNAPSHOT_MONTH] is a date column representing the snapshot month

-- Fetching the CAL_YR_TO_DT_PRIN_PAID_AMT for the immediately preceding snapshot month

SELECT

    A1.APPL_NUM,

    A1.CAL_YR_TO_DT_PRIN_PAID_AMT AS last_mth_prin_paid

FROM

    ACCOUNT_MPL A1

JOIN

    ACCOUNT_MPL A2 ON A1.APPL_NUM = A2.APPL_NUM

WHERE

    A1.SNAPSHOT_MONTH = DATEADD(MONTH, -1, CURRENT_DATE) -- Current snapshot month

    AND A2.SNAPSHOT_MONTH = DATEADD(MONTH, -2, CURRENT_DATE); -- Immediately preceding snapshot month