Access VBA How to use a Union ALL statement - vba

Question

My UNION ALL statement is not returning what I hoped it would. I am putting products into a location (73) and taking them out of the same location. I would like to know how many are remaining in that location. I am trying to figure this out by adding the amount in and subtracting the amount out. I am storing my transactions in tblWarehouseTransfer.
I would like to have one line for each product with the total. What I am getting is one line with the sum of the amount put into the location and one line with the sum of the amount taken out (as a negative number).
I am using a list box to display the list of all my products.
Me.lstCutWipers.RowSource = "SELECT tblProducts.ProductID, tblProducts.ProductName, Sum(tblWarehouseTransfer.Qty) AS SumOfQty " _
& " FROM tblWarehouseTransfer INNER JOIN tblProducts ON tblWarehouseTransfer.ProductID = tblProducts.ProductID " _
& " GROUP BY tblProducts.Productid, tblProducts.ProductName, tblWarehouseTransfer.LocationTo " _
& " HAVING (((tblWarehouseTransfer.LocationTo) = 73)) " _
& " UNION ALL SELECT tblProducts.ProductID, tblProducts.ProductName, -Sum(tblWarehouseTransfer.Qty) AS SumOfQty " _
& " FROM tblWarehouseTransfer INNER JOIN tblProducts ON tblWarehouseTransfer.ProductID = tblProducts.ProductID " _
& " GROUP BY tblProducts.Productid, tblProducts.ProductName, tblWarehouseTransfer.LocationFrom " _
& " HAVING (((tblWarehouseTransfer.LocationFrom)= 73))"
Can someone help me to join the 'in' and the 'out' as one total.

Answer 1

This example joins two subqueries which allows your two different sums to be added together, whereas a UNION only lists rows of the two queries together.
One downside to having subqueries is that it cannot be fully edited in query Design View... it requires the SQL View to edit the whole thing. BUT, you could save each subquery separately and then join those queries together in a third query. Then you could edit each part separately in Design View.
Also notice that I changed the HAVING clause to a WHERE clause. WHERE clauses can be more efficient if you are applying criteria to source values before they are aggregated (i.e. grouped and summed). HAVING applies the criteria after aggregating the data. If the criteria involves aggregate expressions, then they must appear in HAVING clause.
By changing to a WHERE clause it also means that you don't have to group on that field. The difference in speed may be negligible and it should return the same information, but just not necessary since every row contributing to that query will only be for the value in the WHERE clause. Just be aware that if you change the query at all, you need to consider the proper clause to apply criteria.
EDIT: Changed to LEFT JOIN and handled NULL in TotalSum with call to nz().
SELECT ToQuery.ProductID, ToQuery.ProductName, (ToQuery.SumOfQty + nz(FromQuery.SumOfQty, 0.0)) As TotalSum
FROM
(SELECT tblProducts.ProductID, tblProducts.ProductName, Sum(tblWarehouseTransfer.Qty) AS SumOfQty
FROM tblWarehouseTransfer INNER JOIN tblProducts ON tblWarehouseTransfer.ProductID = tblProducts.ProductID
WHERE tblWarehouseTransfer.LocationTo = 73
GROUP BY tblProducts.Productid, tblProducts.ProductName) AS ToQuery
LEFT JOIN
(SELECT tblProducts.ProductID, tblProducts.ProductName, -Sum(tblWarehouseTransfer.Qty) AS SumOfQty
FROM tblWarehouseTransfer INNER JOIN tblProducts ON tblWarehouseTransfer.ProductID = tblProducts.ProductID
WHERE tblWarehouseTransfer.LocationFrom = 73
GROUP BY tblProducts.Productid, tblProducts.ProductName) AS FromQuery
ON ToQuery.ProductID = FromQuery.ProductID
To be complete, this assumes that ProductID is a primary key and that ProductName is unique to each ProductID. If that is not true, you will need to change the outer query ON expression to match ProductName values as well (i.e. add AND ToQuery.ProductName = FromQuery.ProductName).