ACC2000: Sample Function to Create a Running Sum on a Form

This article shows you how to create a sample user-defined function to compute a running sum on a form.

One way to compute a running sum on a form is to use the DSum() function. For additional information about how to use the DSum() function to compute a running sum on a form, please see the following article in the Microsoft Knowledge Base: Using the method demonstrated in this article has the following advantages over using the DSum() function:

• The method demonstrated in this article does not require a sequential ID field. A required sequential ID field limits you to computing a running sum using a single ordering of your records.
• Using the method demonstrated in this article is significantly faster than using the DSum() function to compute a running sum.

How to Create and Use the RunSum() Function

Microsoft provides programming examples for illustration only, without warranty either expressed or implied. This includes, but is not limited to, the implied warranties of merchantability or fitness for a particular purpose. This article assumes that you are familiar with the programming language that is being demonstrated and with the tools that are used to create and to debug procedures. Microsoft support engineers can help explain the functionality of a particular procedure, but they will not modify these examples to provide added functionality or construct procedures to meet your specific requirements. NOTE: The sample code in this article uses Microsoft Data Access Objects. For this code to run properly, you must reference the Microsoft DAO 3.6 Object Library. To do so, click References on the Tools menu in the Visual Basic Editor, and make sure that the Microsoft DAO 3.6 Object Library check box is selected.

1. Open the sample database Northwind.mdb. Create a new module, and type the following line in the Declarations section if it is not already there:

   Option Explicit

2. Type the following code in the module:

   Function RunSum (F As Form, KeyName As String, KeyValue, _
     FieldToSum As String)
   '***********************************************************
   ' FUNCTION: RunSum()
   ' PURPOSE:  Compute a running sum on a form.
   ' PARAMETERS:
   '    F        - The form containing the previous value to
   '               retrieve.
   '    KeyName  - The name of the form's unique key field.
   '    KeyValue - The current record's key value.
   '    FieldToSum - The name of the field in the previous
   '                 record containing the value to retrieve.
   ' RETURNS:  A running sum of the field FieldToSum.
   ' EXAMPLE:  =RunSum(Form,"ID",[ID],"Amount")
   '***********************************************************
      Dim RS As DAO.Recordset
      Dim Result
   
      On Error GoTo Err_RunSum
   
      ' Get the form Recordset.
      Set RS = F.RecordsetClone
   
      ' Find the current record.
      Select Case RS.Fields(KeyName).Type
         ' Find using numeric data type key value?
         Case DB_INTEGER, DB_LONG, DB_CURRENCY, _
            DB_SINGLE, DB_DOUBLE, DB_BYTE
            RS.FindFirst "[" & KeyName & "] = " & KeyValue
         ' Find using date data type key value?
         Case DB_DATE
            RS.FindFirst "[" & KeyName & "] = #" & KeyValue & "#"
         ' Find using text data type key value?
         Case DB_TEXT
            RS.FindFirst "[" & KeyName & "] = '" & KeyValue & "'"
         Case Else
            MsgBox "ERROR: Invalid key field data type!"
            GoTo Bye_RunSum
      End Select
   
      ' Compute the running sum.
      Do Until RS.BOF
         Result = Result + RS(FieldToSum)
   
         ' Move to the previous record.
         RS.MovePrevious
      Loop
   
   Bye_RunSum:
      RunSum = Result
      Exit Function
   
   Err_RunSum:
      Resume Bye_RunSum
   
   End Function

3. Create the following new query based on the Orders table and the Order Subtotals query. Save the query as qryOrders:

      Query: qryOrders
      ------------------------------------------------------
      Type: select query
      Join: Orders.[OrderID] <->; [Order Subtotals].[OrderID]
   
      Field: OrderID
         Table: Orders
         Sort: Ascending
      Field: Subtotal
         Table: Order Subtotals

4. Use the Form Wizard to create a new form based on the qryOrders query. Include both fields on the form. On the next screen click Tabular.
5. Add a text box with the following properties to the new form:

      Name: RunningSum
      ControlSource: =RunSum([Form],"OrderID",[OrderID],"Subtotal")
      Format: Currency

6. Save the form and then view it in Form view.
7. Select different records using the record selector. Note that the RunningSum field shows an accumulated total based on the Subtotal field.