Hello
Try following SQL server Query
DECLARE @EndDate AS DATETIME ='1996-07-30'
DECLARE @StartDate AS DATETIME = CONVERT(VARCHAR(4),YEAR(@EndDate))+'-'+CONVERT(VARCHAR(2),MONTH(@EndDate))+'-01'
SELECT SUM(od.Quantity) FROM Orders AS o
INNER JOIN [Order Details] AS od
ON o.OrderID = od.OrderID
WHERE CONVERT(VARCHAR(10),OrderDate,102)
BETWEEN CONVERT(VARCHAR(10),@StartDate ,102) AND CONVERT(VARCHAR(10),@EndDate ,102)
Check it and let me know your feedback