Question

I’m trying to write a SQL query (SQL Server 2005) to calculate the current value of inventory on hand. I have a table that looks like this:

ID | QTY | BasePrice
1  | 10  | 100
2  | -2  | 0
3  | -2  | 0
4  | 10  | 200
5  | -2  | 0

Where qty > 0 is stock coming in and < 0 is stock going out. Negative quantities don’t record a BasePrice due to other business rules. Base price is price per unit.

I need to find either the average price OR total price of inventory that is still on hand. So the resulting column needs to be:

ID | QTY | BasePrice | TotalPrice | AveragePrice
1  | 10  | 100       | 1000       | 100
2  | -2  | 0         | 800        | 100
3  | -2  | 0         | 600        | 100
4  | 10  | 200       | 2600       | 162.50
5  | -2  | 0         | 2275       | 162.50

I was able to work out this:

select  g1.projectionID,
        g1.qty, 
        g1.basePrice,
        ((sum(isnull(g2.basePrice,0)))) * sum(isnull(g2.Qty,0)) + (g1.Qty * (case when g1.Qty < 0 THEN (sum(isnull(g2.basePrice,0))) ELSE g1.BasePrice END)) As CurrenctValueOfStockOnHand


from test g1
left join test g2 on g2.projectionID < g1.projectionID
group by g1.ProjectionID, g1.Qty, g1.BasePrice

Which gives:

ID| QTY| BasePrice | TotalPrice
1 | 10 | 100.0000  | 1000.0000
2 | -2 | 0.0000    | 800.0000
3 | -2 | 0.0000    | 600.0000
4 | 10 | 200.0000  | 2600.0000
5 | -2 | 0.0000    | 4200.0000

But as you can see it gives the wrong values after the 2nd lot of inventory is added (after ID 4).

We currently have C# code that loops through each record and keeps a running total. For large stocks this takes far too long. If the only option is to use a cursor then we’ll keep our C# code.

Answer 1

After Randy mentioned using LAG function I had a quick Google search for LAG function in SQL Server and found code using a table variable and an update statement.

declare @TempStocks TABLE (ProjectionID int, Qty Int, BasePrice Decimal (18,4), runningQty int, totalValueOfStockOnHand decimal(18,4))

insert into @TempStocks
select g1.*, sum(isnull(g2.Qty, 0)) + g1.Qty, 0
from gregTest g1
left join gregTest g2 on g2.projectionID < g1.ProjectionID
group by g1.ProjectionID, g1.BasePRice, g1.Qty

select * from @TempStocks

declare @CurrentValue Decimal (18,4)

set @CurrentValue = 0

update @TempStocks
set @CurrentValue = TotalValueOfStockOnHand = case when (Qty > 0) THEN (@CurrentValue + (BasePrice * Qty)) ELSE @CurrentValue + ((@CurrentValue / (RunningQty - qty) * Qty)) END

select *, TotalValueOfStockOnHand / RunningQty from @TempStocks

I’m still not convinced this is the best answer, but it does give the correct output without using a cursor