30天滚动总和

Question

我正在寻找一个SQL查询来完成类似this的操作 在这里，我能够编写查询以获取运行总计，但在30天汇总中遇到了困难。如果有人可以帮助我，那就太好了。

这是我的查询

SELECT
   t.merchant_id,
   t.DAY as transaction_date,
   t.daily_transaction_total,
   @running_total: = @running_total + t.daily_transaction_total AS rolling_30_day_total 
FROM
   (
      SELECT
         MERCHANT_ID,
         date(EVENT_TIMESTAMP) as day,
         SUM(VALUE) as daily_transaction_total 
      FROM
         MERCHANT_TRANSACTION_EVENT_LOG 
      GROUP BY
         day,
         MERCHANT_ID 
   )
   t 
   JOIN
      (
         SELECT
            @running_total: = 0
      )
      r 
where
   merchant_id = 3 
ORDER BY
   merchant_id,
   t.day;