En måde at undgå dette på (med forbehold for RDBMS-understøttelse) ville være
WITH R
AS (SELECT *,
Sum(HeadCount) OVER (PARTITION BY date) AS SumHeadCount
FROM Report)
SELECT R.date,
SumHeadCount,
Sum(P.Quantity) AS SumQuantity
FROM R
JOIN Production P
ON R.ReportID = P.ReportID
GROUP BY R.date, SumHeadCount
ORDER BY R.date