I did some googling and research and got this as allowing me to do a group by trailing 60 row sum.

WITH CTE AS (
  SELECT
    EVENT_DATE
    , CUSTOMERID
    , COUNT(*) AS NumberOfViews
  FROM TABLE
  AND EVENT_DATE >= DATEADD(DAY, -360, GETDATE())
  GROUP BY EVENT_DATE, CUSTOMERID
)

SELECT
  EVENT_DATE
  , CUSTOMERID
  , SUM(NumberOfViews) OVER (PARTITION BY CUSTOMERID ORDER BY EVENT_DATE ASC ROWS BETWEEN 60 PRECEDING AND CURRENT ROW) AS NumberOfViews60D
FROM CTE
ORDER BY
    CUSTOMERID, EVENT_DATE;

Which works fine! However, I want the rolling 60 day sum, not 60 row sum. I got this as an answer but it doesn’t work. What should I do?

WITH CTE AS (
  SELECT
    EVENT_DATE
    , CUSTOMERID
    , COUNT(*) AS NumberOfViews
  FROM TABLE
  AND EVENT_DATE >= DATEADD(DAY, -360, GETDATE())
  GROUP BY EVENT_DATE, CUSTOMERID
)

SELECT
  EVENT_DATE
  , CUSTOMERID
  , SUM(NumberOfViews) OVER (PARTITION BY CUSTOMERID ORDER BY EVENT_DATE ASC RANGE BETWEEN INTERVAL '60 DAY' PRECEDING AND CURRENT ROW) AS NumberOfViews60D
FROM CTE
ORDER BY
    CUSTOMERID, EVENT_DATE;