SQL Server : calculate monthly total sales incl empty months

Question

I\'m trying to calculate the total sales of a product in a month, but I would like it to include any \"empty\" months (with no sales) and only select the latest 12 months.

Answer 1

I've done before I know that you have calendar table. I've used master.dbo.spt_values to generate last twelve consecutive months (including current).

    declare @ProductNo int

    set @ProductNo = 1234

select MONTH(d.date), YEAR(d.date), isnull(t.amnt, 0) as [Units sold] from (
    SELECT
        YEAR(o.OrderDate) as 'Year', 
        MONTH(o.OrderDate) as 'Month', 
        sum(Amount) as amnt,
        [ProductNo]
    FROM [OrderLine] ol
    inner join [Order] o on ol.OrderNo = o.OrderNo
    where ProductNo = @ProductNo
    group by ProductNo, YEAR(o.OrderDate), Month(o.OrderDate)
) t
right join (
    select dateadd(mm, -number, getdate()) as date
    from master.dbo.spt_values 
    where type = 'p' and number < 12
) d  on year(d.date) = t.[year] and month(d.date) = t.[month]
order by YEAR(d.date), MONTH(d.date)