ACC2000: How to Create a Grouped Running Sum in a Query

The preferred method for producing running sums per group is to create an Access report. However, you can produce similar running sums in a query. The following example shows how you can create a running sum on a group of items in an Access query.

1. Open the sample database, Northwind.mdb.
2. Create the following new query based on the Products table.

   
      Query: qryGrpRunSum
      -------------------
      Type: Select Query
   
      Field: CategoryID
      Table: Products
      Sort:  Ascending
   
      Field: UnitsInStock
      Table: Products
    

3. In the Field row of the third column in the query design grid, type the following expression:

   RunSum: fncRunSum([CategoryID], [UnitsInStock])
   

4. Save the query as qryGrpRunSum, and then close the query.
5. Create a new module, and then type or paste the following code:

   Option Compare Database
   Option Explicit
   
   Function fncRunSum(lngCatID As Long, lngUnits As Long) As Long
       'Variables that retain their values.
       Static lngID As Long
       Static lngAmt As Long
   
       If lngID <> lngCatID Then
           'If the current ID does not match the last ID, then (re)initialize.
           lngID = lngCatID
           lngAmt = lngUnits
       Else
           'If the current ID matches the last, keep a running sum for the ID.
           lngAmt = lngAmt + lngUnits
       End If
   
       'Pass the running sum back to the query.
       fncRunSum = lngAmt
   End Function
   

6. Save the module as modGrpRunSum, and then close the module.
7. In the Database window, double-click the qryGrpRunSum query to run the query. Note that the first column of the query displays the categories, the second column displays the units in stock, and the third column displays a running sum of the units in stock per category.

IMPORTANT: If you scroll up or down in Datasheet view of the query, the running sum values may change. This is expected behavior with this type of an Access query and with Microsoft Jet. If this occurs, scroll to the group that you want to view, and press F9 once or twice to accurately recalculate the sum for the group that is being displayed. You can also include criteria in the query to return only the group for which you want to see a running sum.