Return All Months & Years Between Date Range – SQL

I’m a bit stumped how I might go about this.

I have a very basic query, that currently returns sales for each product, by year and month. It is grouping by year/month, and summing up the quantity. This returns one row for each product/year/month combo where there was a sale.

If there was no sale for a month, then there is no data.

I’d like my query to return one row of data for each product for each year/month in my date range, regardless of whether there was actually an order.

If there was no order, then I can return 0 for that product/year/month.

Below is my example query.

Declare @DateFrom datetime, @DateTo Datetime
Set @DateFrom = '2012-01-01'
set @DateTo = '2013-12-31'

select 
Convert(CHAR(4),order_header.oh_datetime,120) + '/' + Convert(CHAR(2),order_header.oh_datetime,110) As YearMonth,
variant_detail.vad_variant_code,
sum(order_line_item.oli_qty_required) as 'TotalQty'

From 
variant_Detail
join order_line_item on order_line_item.oli_vad_id = variant_detail.vad_id
join order_header on order_header.oh_id = order_line_item.oli_oh_id

Where 
(order_header.oh_datetime between @DateFrom and @DateTo)

Group By 
Convert(CHAR(4),order_header.oh_datetime,120) + '/' + Convert(CHAR(2),order_header.oh_datetime,110),
variant_detail.vad_variant_code

Answer

Thank your for your suggestions.

I managed to get this working using another method.

Declare @DateFrom datetime, @DateTo Datetime
Set @DateFrom = '2012-01-01'
set @DateTo = '2013-12-31'

select 
YearMonthTbl.YearMonth,
orders.vad_variant_code,
orders.qty

From 
(SELECT  Convert(CHAR(4),DATEADD(MONTH, x.number, @DateFrom),120) + '/' + Convert(CHAR(2),DATEADD(MONTH, x.number, @DateFrom),110) As YearMonth
FROM    master.dbo.spt_values x
WHERE   x.type = 'P'        
AND     x.number <= DATEDIFF(MONTH, @DateFrom, @DateTo)) YearMonthTbl


left join 
    (select variant_Detail.vad_variant_code, 
    sum(order_line_item.oli_qty_required) as 'Qty', 
    Convert(CHAR(4),order_header.oh_datetime,120) + '/' + Convert(CHAR(2),order_header.oh_datetime,110) As 'YearMonth'
    FROM order_line_item 
    join variant_detail on variant_detail.vad_id = order_line_item.oli_vad_id
    join order_header on order_header.oh_id = order_line_item.oli_oh_id
    Where 
    (order_header.oh_datetime between @DateFrom and @DateTo)
    GROUP BY variant_Detail.vad_variant_code,
    Convert(CHAR(4),order_header.oh_datetime,120) + '/' + Convert(CHAR(2),order_header.oh_datetime,110)
    ) as Orders on Orders.YearMonth = YearMonthTbl.YearMonth