Microsoft KB Archive/101081

= ACC: Referring to a Field in the Previous or Next Record =

Article ID: 101081

Article Last Modified on 1/18/2007

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APPLIES TO


 * Microsoft Access 1.0 Standard Edition
 * Microsoft Access 1.1 Standard Edition
 * Microsoft Access 2.0 Standard Edition
 * Microsoft Access 95 Standard Edition
 * Microsoft Access 97 Standard Edition

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This article was previously published under Q101081





SUMMARY
Advanced: Requires expert coding, interoperability, and multiuser skills.

This article shows you two methods that you can use to obtain values from the previous or the next record for use in calculations. The first method uses the DLookupfunction in an expression; the second method uses two user-defined functions.

NOTE: A demonstration of the technique used in this article can be seen in the sample file, Qrysmp97.exe. For information about how to obtain this sample file, please see the following article in the Microsoft Knowledge Base:

182568 ACC97: Microsoft Access 97 Sample Queries Available in Download Center



Using DLookup
NOTE: This technique assumes you have a table with an ID field of a Number data type, and the ID values are not missing any number in sequential order. If your table does not meet these criteria, then you should use the "Using Code" method described later in this article.

You can use the following sample DLookup expressions to obtain values from a field in the previous or next record of a form, a report, or a query.

In a Form:
To obtain a value from a field in the previous record, type the following line for the text box's ControlSource property: =DLookUp("[Field]","Table","[ID]=Forms![Form1]![ID]-1") To obtain a value from a field in the next record, type the following line for the text box's ControlSource property: =DLookUp("[Field]","Table","[ID]=Forms![Form1]![ID]+1")

In a Report:
To obtain a value from a field in the previous record, type the following line for the text box's ControlSource property: =DLookUp("[Field]","Table","[ID]=Reports![Report1]![ID]-1") To obtain a value from a field in the next record, type the following line for the text box's ControlSource property: =DLookUp("[Field]","Table","[ID]=Reports![Report1]![ID]+1")

In a Query:
To obtain a value from a field in the previous record, type the following line in the Field row of the query grid: Expr1: DLookUp("[Field1]","Table1","[ID]=" & [ID]-1) To obtain a value from a field in the next record, type the following line in the Field row of the query grid: Expr1: DLookUp("[Field1]","Table1","[ID]=" & [ID]+1) NOTE: In these sample expressions, the "-1" and "+1" indicate the previous and next records. When the current record is the first record in the recordset, the "-1" returns a Null value because there is no previous record. Likewise, when the current record is the last record in the recordset, the "+1" returns a Null. If you want to return a value from a record other than the next or previous one, you can specify a different number, for example, "-3" for the third previous record.

Using Code
This section assumes that you are familiar with Visual Basic for Applications and with creating Microsoft Access applications using the programming tools provided with Microsoft Access. For more information about Visual Basic for Applications, please refer to your version of the "Building Applications with Microsoft Access" manual.

NOTE: Visual Basic for Applications is called Access Basic in Microsoft Access version 1.x and Microsoft Access version 2.0.

To retrieve a value in a field from the previous or next record in a form by using code, follow these steps:

 Create a new module and type the following line in the Declarations section if it is not already there:

Option Explicit

  Type the following procedures:

NOTE: In the following sample code, an underscore (_) at the end of a line is used as a line-continuation character. If you are using a version of Microsoft Access earlier than 7.0, remove the underscore from the end of the line when re-creating this code. '*************************************************************     ' FUNCTION: PrevRecVal ' PURPOSE: Retrieve a value from a field in the previous form '         record. ' PARAMETERS: '   F        - The form from which to get the previous value. '   KeyName  - The name of the form's unique key field. '   KeyValue - The current record's key value. '   FieldNameToGet - The name of the field in the previous '                    record from which to retrieve the value. ' RETURNS: The value in the field FieldNameToGet from the '         previous form record. ' EXAMPLE: '   =PrevRecVal(Form,"ID",[ID],"OdometerReading") '**************************************************************        Function PrevRecVal (F As Form, KeyName As String, KeyValue, _         FieldNameToGet As String) Dim RS As Recordset

On Error GoTo Err_PrevRecVal

' The default value is zero. PrevRecVal = 0

' 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!" Exit Function End Select

' Move to the previous record. RS.MovePrevious

' Return the result. PrevRecVal = RS(FieldNameToGet)

Bye_PrevRecVal: Exit Function Err_PrevRecVal: Resume Bye_PrevRecVal End Function

'*************************************************************     ' FUNCTION: NextRecVal ' PURPOSE: Retrieve a value from a field in the next form '         record. '**************************************************************        Function NextRecVal (F As Form, KeyName As String, KeyValue, _         FieldNameToGet As String) Dim RS As Recordset

On Error GoTo Err_NextRecVal

' The default value is zero. NextRecVal = 0

' 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!" Exit Function End Select

' Move to the next record. RS.MoveNext

' Return the result. NextRecVal = RS(FieldNameToGet)

Bye_NextRecVal: Exit Function Err_NextRecVal: Resume Bye_NextRecVal End Function 

The following example demonstrates how to use the PrevRecVal function in a form to create a mileage log. The custom function returns the previous odometer reading, which is used to calculate miles per gallon (MPG) for an automobile. To use the PrevRecVal function, follow these steps:

  Create the following new table, and then save it as Mileage Log:      Table: Mileage Log -     Field Name: ID         Data Type : AutoNumber (or Counter in Access 2.0 or earlier) Indexed: Yes (No Duplicates) Field Name: Date Data Type : Date/Time Field Name: Odometer Data Type : Number FieldSize: Double Field Name: Gallons Data Type : Number FieldSize: Double Primary Key: ID   View the Mileage Log table in Datasheet view and enter the following sample data:      ID   Date      Odometer   Gallons -     1    6/21/94   77917.8    10.2      2    6/25/94   78254.7    9.6      3    6/30/94   78582.3    10      4    7/5/94    78918.4    10.4      5    7/10/94   79223.4    9.4 </li> Use the Form Wizard to create a new tabular form based on the Mileage Log table. Include all the Mileage Log table fields, except the ID field.</li>  View the form in Design view and add the following three text box controls to the form: <pre class="fixed_text">     Text Box 1 -     Name: PrevOdometer ControlSource: =PrevRecVal(Form,"ID",[ID],"Odometer") Format: Fixed

Text Box 2 -     Name: MilesDriven ControlSource: =iif([PrevOdometer]=0,0,[Odometer]-[PrevOdometer]) Format: Fixed

Text Box 3 ---     Name: MPG ControlSource: =[MilesDriven]/[Gallons] Format: Fixed </li>  View the form in Form view. Note that the form displays the following information: <pre class="fixed_text">     Date     Odometer   Gallons  PrevOdometer  MilesDriven  MPG -     6/21/94  77917.8    10.2     0             0            0      6/25/94  78254.7     9.6     77917.80      336.90       35.09      6/30/94  78582.3    10.0     78254.70      327.60       32.76      7/05/94  78918.4    10.4     78582.30      336.10       32.32      7/10/94  79223.4     9.4     78918.40      305.00       32.45 </li></ol>

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