Write a query to calculate moving average of last 7 days.

Short answer: Use AVG(Amount) OVER (ORDER BY OrderDate ROWS BETWEEN 6 PRECEDING AND CURRENT ROW).

Sample solution

SELECT OrderDate, Amount,
       AVG(Amount * 1.0) OVER (
           ORDER BY OrderDate
           ROWS BETWEEN 6 PRECEDING AND CURRENT ROW
       ) AS MovingAvg7
FROM DailySales;

ROWS vs RANGE matters when OrderDate has duplicates.