Summarise by week, even for empty rows

Question

I want to summarise the sum of sales.quantity by week, and to show the week number even if there are no sales.

I have setup a weeks table with 1-54 in there to use an ou

Answer 1

The where clause WHERE (sales.transDate BETWEEN @fromDate AND @toDate) will remove any weeks without sales. You'll likely need to do a subquery to pull the transactions and then join that to your weeks table.

SELECT Weeks.WeekNum, SUM(sales.quantity) AS sales
FROM Weeks LEFT OUTER JOIN 
 (
    SELECT *
    FROM sales 
    WHERE (sales.transDate BETWEEN @fromDate AND @toDate)
 ) sales
    ON Weeks.WeekNum = DATEPART(week, sales.transDate)
GROUP BY Weeks.WeekNum