SELECT 
YEAR_MONTH,
MONTH_AMT,
SUM(MONTH_AMT) OVER(ORDER BY YEAR_MONTH ROWS UNBOUNDED PRECEDING) AS CUML_AMT
FROM
(SELECT DISTINCT substr(SALES_DATE,1,7) AS YEAR_MONTH
,SUM(SALES_AMT) OVER (PARTITION BY substr(SALES_DATE,1,7)) AS MONTH_AMT
FROM SALES
WHERE UPDATED_NO IS NULL)
WHERE YEAR_MONTH BETWEEN '2023-01' AND '2023-12'
ORDER BY YEAR_MONTH;