Microsoft KB Archive/325685

= HOW TO: Implement a DataSet GROUP BY Helper Class in Visual Basic .NET =

Article ID: 325685

Article Last Modified on 9/4/2003

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APPLIES TO


 * Microsoft .NET Framework 1.1 Service Pack 1
 * Microsoft ADO.NET 1.1
 * Microsoft Visual Basic .NET 2002 Standard Edition
 * Microsoft Visual Basic .NET 2003 Standard Edition

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This article was previously published under Q325685





For a Microsoft Visual C# .NET version of this article, see 326145.

This article refers to the following Microsoft .NET Framework Class Library namespace:
 * System.Data



Note This article is one of a series of DataSetHelper articles. You can merge the code in the DataSetHelper class that is listed in this article with the code that is provided in other DataSetHelper articles to make a single class with a more comprehensive feature set.

Click here to view the complete list of DataSetHelper articles

This article refers to the following Microsoft .NET Framework Class Library namespace:
 * System.Data

IN THIS TASK

 * SUMMARY
 * Requirements
 * DataSetHelper Shell Class
 * Field List Parsers
 * CreateGroupByTable Method
 * InsertGroupByInto Method
 * SelectGroupByInto Method
 * Test the Application
 * Enhancement Ideas
 * Troubleshooting



SUMMARY
This step-by-step article describes how to implement and how to use a DataSetHelper class that includes sample code to create a DataTable object that contains aggregate data (including optional rollup totals similar to the Microsoft SQL Server WITH ROLLUP keyword) from another DataTable object.

To do this, use the following public methods:
 * CreateGroupByTable
 * InsertGroupByInto
 * SelectGroupByInto

The SelectGroupByInto method calls the CreateGroupByTable method and the InsertGroupByInto method. You can also use private helper methods and data members to store the parsed field list and to handle NULL values correctly when the aggregate values are calculated.

The DataSetHelper class includes a DataSet member variable. Optionally, you can assign an existing DataSet to the DataSet member variable. If the member variable points to a valid DataSet, any DataTable objects that the CreateGroupByTable or the SelectGroupByInto method creates are added to the DataSet. In either case, the method call returns a reference to the DataTable object. The InsertGroupByInto method requires an existing target DataTable and does not return anything.

For additional information about DataSet objects, click the following article number to view the article in the Microsoft Knowledge Base:

313485 INFO: Roadmap for ADO.NET DataSet, DataView, and DataViewManager Objects

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Requirements
The following list outlines the recommended hardware, software, network infrastructure, and service packs that are required:
 * Microsoft Windows XP, Windows 2000, or Windows NT 4.0 Service Pack 6a
 * Microsoft Visual Studio .NET

This article assumes that you are familiar with the following topics:
 * Visual Basic .NET syntax
 * ADO.NET fundamentals and syntax

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DataSetHelper Shell Class
The code in this section declares the shell class that all DataSetHelper articles add methods and member variables to.  Start Visual Studio .NET. On the File menu, point to New, and then click Project. In the New Project dialog box, click Visual Basic Projects under Project Types, and then click Class Library under Templates. In the Name box, type DataSetHelper .  Replace the class code with the following code: Public Class DataSetHelper Public ds As DataSet

Public Sub New(ByVal DataSet As DataSet) ds = DataSet End Sub

Public Sub New ds = Nothing End Sub

End Class You can use the two overloads for the constructor to create an instance of the class with or without a reference to a valid DataSet. For a class that contains a reference to a valid DataSet, the DataTable objects that the methods return are also added automatically to the DataSet. </ol>

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Field List Parsers
This section contains the code for two field list parsers: one for the field list, and one for the fields to group by. The parsed structure is used so that the CreateGroupByTable and the InsertGroupByInto methods do not have to reparse the field list. These methods must reparse the field list if they are called from the SelectGroupByInto method or from your own code. The parsed field list and the unparsed field list are stored in Private member variables of the DataSetHelper class. <ol>  Add the following Private class definition in the DataSetHelper class that you created in the &quot;DataSetHelper Shell Class&quot; section: Private Class FieldInfo Public RelationName As String Public FieldName As String     ' source table field name Public FieldAlias As String    ' destination table field name Public Aggregate As String End Class Note This class is common to other DataSetHelper articles, and contains some fields that this article does not use. </li>  Add the following Private member variables to the class definition immediately after the DataSet declaration: Private m_FieldInfo As ArrayList, m_FieldList As String Private GroupByFieldInfo As ArrayList, GroupByFieldList As String </li>  Add the following Private method to the class definition. This method is the same as the method that is used in other DataSetHelper articles and is used to parse the list of fields to group by. Private Sub ParseFieldList(ByVal FieldList As String, Optional ByVal AllowRelation As Boolean = False) '   ' Parses FieldList into FieldInfo objects and then adds them to the m_FieldInfo private member '   ' FieldList syntax: [relationname.]fieldname[ alias],... '   If m_FieldList = FieldList Then Exit Sub m_FieldInfo = New ArrayList m_FieldList = FieldList Dim Field As FieldInfo, FieldParts As String, Fields As String = FieldList.Split(&quot;,&quot;) Dim I As Integer For I = 0 To Fields.Length - 1 Field = New FieldInfo '       ' Parse FieldAlias '       FieldParts = Fields(I).Trim.Split(&quot; &quot;) Select Case FieldParts.Length Case 1 ' To be set at the end of the loop Case 2 Field.FieldAlias = FieldParts(1) Case Else Throw New ArgumentException(&quot;Too many spaces in field definition: '&quot; & Fields(I) & &quot;'.&quot;) End Select '       ' Parse FieldName and RelationName '       FieldParts = FieldParts(0).Split(&quot;.&quot;) Select Case FieldParts.Length Case 1 Field.FieldName = FieldParts(0) Case 2 If Not AllowRelation Then _ Throw New ArgumentException(&quot;Relation specifiers not allowed in field list: '&quot; & Fields(I) & &quot;'.&quot;) Field.RelationName = FieldParts(0).Trim Field.FieldName = FieldParts(1).Trim Case Else Throw New ArgumentException(&quot;Invalid field definition: '&quot; & Fields(I) & &quot;'.&quot;) End Select If Field.FieldAlias = &quot;&quot; Then Field.FieldAlias = Field.FieldName m_FieldInfo.Add(Field) Next End Sub </li>  Add the following Private method to the class definition. This method is used to parse the field list, including aggregate functions. Private Sub ParseGroupByFieldList(ByVal FieldList As String) '   ' Parses FieldList into FieldInfo objects and then adds them to the GroupByFieldInfo private member '   ' FieldList syntax: fieldname[ alias]|operatorname(fieldname)[ alias],... '   ' Supported Operators: count,sum,max,min,first,last '   If GroupByFieldList = FieldList Then Exit Sub Const OperatorList As String = &quot;,count,sum,max,min,first,last,&quot; GroupByFieldInfo = New ArrayList Dim Field As FieldInfo, FieldParts As String, Fields As String = FieldList.Split(&quot;,&quot;) Dim I As Integer For I = 0 To Fields.Length - 1 Field = New FieldInfo '       ' Parse FieldAlias '       FieldParts = Fields(I).Trim.Split(&quot; &quot;) Select Case FieldParts.Length Case 1 ' To be set at the end of the loop Case 2 Field.FieldAlias = FieldParts(1) Case Else Throw New ArgumentException(&quot;Too many spaces in field definition: '&quot; & Fields(I) & &quot;'.&quot;) End Select '       ' Parse FieldName and Aggregate '       FieldParts = FieldParts(0).Split(&quot;(&quot;)        Select Case FieldParts.Length            Case 1                Field.FieldName = FieldParts(0)            Case 2                Field.Aggregate = FieldParts(0).Trim.ToLower ' You will do a case-sensitive comparison later.                Field.FieldName = FieldParts(1).Trim(&quot; &quot;c, &quot;)&quot;c) Case Else Throw New ArgumentException(&quot;Invalid field definition: '&quot; & Fields(I) & &quot;'.&quot;) End Select If Field.FieldAlias = &quot;&quot; Then If Field.Aggregate = &quot;&quot; Then Field.FieldAlias = Field.FieldName Else Field.FieldAlias = Field.Aggregate & &quot;Of&quot; & Field.FieldName End If       End If        GroupByFieldInfo.Add(Field) Next GroupByFieldList = FieldList End Sub </li></ol>

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CreateGroupByTable Method
This section contains the code for the CreateGroupByTable method

The following is the calling convention for the CreateGroupByTable method: dt = dsHelper.CreateGroupByTable(&quot;OrderSummary&quot;, ds.Tables!Orders, &quot;EmployeeID,sum(Amount) Total,min(Amount) Min,max(Amount) Max&quot;) This call sample creates a new DataTable with a TableName of OrderSummary and four fields (EmployeeID, Total, Min, and Max). The four fields have the same data type as the EmployeeID and the Amount fields in the Orders table.

Use the following syntax to specify fields in the field list: fieldname[ alias]|aggregatefunction(fieldname)[ alias], ... Note the following for this syntax:
 * The ColumnName and the DataType properties are the only properties that are copied to the destination DataTable.
 * You can rename a field in the destination DataTable by specifying an alias name.
 * The field list can contain a subset of field names that are listed in a different order than in the source DataTable. If the field list is blank, an exception is thrown.
 * Relation specifiers are not supported as part of the field name. All fields must come from the same DataTable.

To call the CreateGroupByTable method, add the following method to the DataSetHelper class that you created in the &quot;DataSetHelper Shell Class&quot; section: Public Function CreateGroupByTable(ByVal TableName As String, _                                  ByVal SourceTable As DataTable, _                                   ByVal FieldList As String) As DataTable '   ' Creates a table based on aggregates of fields of another table '   ' RowFilter affects rows before the GroupBy operation. No HAVING-type support ' although this can be emulated by later filtering of the resultant table. '   ' FieldList syntax: fieldname[ alias]|aggregatefunction(fieldname)[ alias], ... '   If FieldList = &quot;&quot; Then Throw New ArgumentException(&quot;You must specify at least one field in the field list.&quot;) ' Return CreateTable(TableName, SourceTable) Else Dim dt As New DataTable(TableName) ParseGroupByFieldList(FieldList) Dim Field As FieldInfo, dc As DataColumn For Each Field In GroupByFieldInfo dc = SourceTable.Columns(Field.FieldName) If Field.Aggregate = &quot;&quot; Then dt.Columns.Add(Field.FieldAlias, dc.DataType, dc.Expression) Else dt.Columns.Add(Field.FieldAlias, dc.DataType) End If       Next If Not ds Is Nothing Then ds.Tables.Add(dt) Return dt   End If End Function back to the top

InsertGroupByInto Method
This section contains code for the InsertGroupByInto method. This code copies records that are sorted and filtered from the source table and related tables to the destination table. The filter is applied before any aggregate values are calculated. If the Rollup argument is True, group totals and grand totals are added for each field in the GroupBy argument. When you perform a Rollup, if you also want detail records to be included, add the primary key field to the end of the list of fields in the GroupBy argument.

The results are sorted on the fields that are listed in the GroupBy argument. The GroupBy argument must comply with a valid Sort field list (minus ASC and DESC modifiers). If the GroupBy argument is blank, the target DataTable contains only a single record that aggregates all the input. When you call the ParseGroupByFieldList and the ParseFieldList properties, you can parse lists that were previously parsed, if these lists are available. If the field list is blank, an exception is thrown.

This is the calling convention for the InsertGroupByInto method: dsHelper.InsertGroupByInto(ds.Tables!OrderSummary, ds.Tables!Orders, &quot;EmployeeID,sum(Amount) Total,min(Amount) Min,max(Amount) Max&quot;, &quot;EmployeeID<5&quot;, &quot;EmployeeID&quot;) This call sample reads records from the DataTable that is named Orders and writes records to the DataTable that is named OrderSummary. The OrderSummary DataTable contains the EmployeeID field and three different aggregates of the Amount field that are filtered on &quot;EmployeeID<5&quot; and that are grouped on (and sorted by) EmployeeID.

Note The filter expression is applied before any aggregate functionality. To implement HAVING-type functionality, filter the DataTable that results.

To call the InsertGroupByInto method, add the following method to the DataSetHelper class that you created in the &quot;DataSetHelper Shell Class&quot; section: Public Sub InsertGroupByInto(ByVal DestTable As DataTable, _                            ByVal SourceTable As DataTable, _                             ByVal FieldList As String, _                             Optional ByVal RowFilter As String = &quot;&quot;, _                             Optional ByVal GroupBy As String = &quot;&quot;, _                             Optional ByVal Rollup As Boolean = False) '   ' Copies the selected rows and columns from SourceTable and inserts them into DestTable ' FieldList has same format as CreateGroupByTable '   ParseGroupByFieldList(FieldList)  ' parse field list ParseFieldList(GroupBy)          ' parse field names to Group By into an arraylist Dim Field As FieldInfo Dim Rows As DataRow = SourceTable.Select(RowFilter, GroupBy) Dim SourceRow, LastSourceRow As DataRow, SameRow As Boolean, I As Integer, J As Integer, K As Integer Dim DestRows(m_FieldInfo.Count) As DataRow, RowCount(m_FieldInfo.Count) As Integer '   ' Initialize Grand total row '   DestRows(0) = DestTable.NewRow '   ' Process source table rows '   For Each SourceRow In Rows '       ' Determine whether we've hit a control break '       SameRow = False If Not (LastSourceRow Is Nothing) Then SameRow = True For I = 0 To m_FieldInfo.Count - 1 ' fields to Group By               Field = m_FieldInfo(I) If ColumnEqual(LastSourceRow(Field.FieldName), SourceRow(Field.FieldName)) = False Then SameRow = False Exit For End If           Next I            ' ' Add previous totals to the destination table '           If Not SameRow Then For J = m_FieldInfo.Count To I + 1 Step -1 '                   ' Make NULL the key values for levels that have been rolled up                    ' For K = m_FieldInfo.Count - 1 To J Step -1 Field = LocateFieldInfoByName(GroupByFieldInfo, m_FieldInfo(K).FieldName) If Not (Field Is Nothing) Then  ' Group By field does not have to be in field list DestRows(J)(Field.FieldAlias) = DBNull.Value End If                   Next K                    ' ' Make NULL any non-aggregate, non-group-by fields in anything other than ' the lowest level. '                   If J <> m_FieldInfo.Count Then For Each Field In GroupByFieldInfo If Field.Aggregate <> &quot;&quot; Then Exit For If LocateFieldInfoByName(m_FieldInfo, Field.FieldName) Is Nothing Then DestRows(J)(Field.FieldAlias) = DBNull.Value End If                       Next End If                   ' ' Add row '                   DestTable.Rows.Add(DestRows(J)) If Rollup = False Then Exit For ' only add most child row if not doing a roll-up Next J           End If        End If        ' ' create new destination rows ' Value of I comes from previous If block '       If Not SameRow Then For J = m_FieldInfo.Count To I + 1 Step -1 DestRows(J) = DestTable.NewRow RowCount(J) = 0 If Rollup = False Then Exit For Next J       End If        For J = 0 To m_FieldInfo.Count RowCount(J) += 1 For Each Field In GroupByFieldInfo Select Case Field.Aggregate ' this test is case-sensitive - made lower-case by Build_GroupByFiledInfo Case &quot;&quot;   ' implicit Last DestRows(J)(Field.FieldAlias) = SourceRow(Field.FieldName) Case &quot;last&quot; DestRows(J)(Field.FieldAlias) = SourceRow(Field.FieldName) Case &quot;first&quot; If RowCount(J) = 1 Then DestRows(J)(Field.FieldAlias) = SourceRow(Field.FieldName) Case &quot;count&quot; DestRows(J)(Field.FieldAlias) = RowCount(J) Case &quot;sum&quot; DestRows(J)(Field.FieldAlias) = Add(DestRows(J)(Field.FieldAlias), SourceRow(Field.FieldName)) Case &quot;max&quot; DestRows(J)(Field.FieldAlias) = Max(DestRows(J)(Field.FieldAlias), SourceRow(Field.FieldName)) Case &quot;min&quot; If RowCount(J) = 1 Then DestRows(J)(Field.FieldAlias) = SourceRow(Field.FieldName) ' so we get by initial NULL Else DestRows(J)(Field.FieldAlias) = Min(DestRows(J)(Field.FieldAlias), SourceRow(Field.FieldName)) End If               End Select Next Next J       LastSourceRow = SourceRow Next If Rows.Length > 0 Then '       ' Make NULL the key values for levels that have been rolled up        ' For J = m_FieldInfo.Count To 0 Step -1 For K = m_FieldInfo.Count - 1 To J Step -1 Field = LocateFieldInfoByName(GroupByFieldInfo, m_FieldInfo(K).FieldName) If Not (Field Is Nothing) Then ' Group By field does not have to be in field list DestRows(J)(Field.FieldAlias) = DBNull.Value End If           Next K            ' ' Make NULL any non-aggregate, non-group-by fields in anything other than ' the lowest level. '           If J <> m_FieldInfo.Count Then For Each Field In GroupByFieldInfo If Field.Aggregate <> &quot;&quot; Then Exit For If LocateFieldInfoByName(m_FieldInfo, Field.FieldName) Is Nothing Then DestRows(J)(Field.FieldAlias) = DBNull.Value End If               Next End If           ' ' Add row '           DestTable.Rows.Add(DestRows(J)) If Rollup = False Then Exit For Next J   End If End Sub

Private Function LocateFieldInfoByName(ByVal FieldList As ArrayList, ByVal Name As String) As FieldInfo '   ' Looks up a FieldInfo record based on FieldName '   Dim Field As FieldInfo For Each Field In FieldList If Field.FieldName = Name Then Return Field Next End Function

Private Function ColumnEqual(ByVal A As Object, ByVal B As Object) As Boolean '   ' Compares two values to determine if they are equal. Also compares DBNULL.Value. '   ' NOTE: If your DataTable contains object fields, you must extend this ' function to handle them in a meaningful way if you intend to group on them. '   If A Is DBNull.Value And B Is DBNull.Value Then Return True ' Both are DBNull.Value. If A Is DBNull.Value Or B Is DBNull.Value Then Return False ' Only one is DbNull.Value. Return A = B                                               ' Value type standard comparison End Function

Private Function Min(ByVal A As Object, ByVal B As Object) As Object '   ' Returns MIN of two values. DBNull is less than all others. '   If A Is DBNull.Value Or B Is DBNull.Value Then Return DBNull.Value If A < B Then Return A Else Return B End Function

Private Function Max(ByVal A As Object, ByVal B As Object) As Object '   ' Returns Max of two values. DBNull is less than all others. '   If A Is DBNull.Value Then Return B    If B Is DBNull.Value Then Return A    If A > B Then Return A Else Return B End Function

Private Function Add(ByVal A As Object, ByVal B As Object) As Object '   ' Adds two values. If one is DBNull, returns the other. '   If A Is DBNull.Value Then Return B    If B Is DBNull.Value Then Return A    Return A + B End Function back to the top

SelectGroupByInto Method
This section contains the code for the SelectGroupByInto method. This method is a combination of the CreateGroupByTable and the InsertGroupByInto methods. The SelectGroupByInto method creates a new DataTable based on existing DataTable objects, and copies the records that are sorted and filtered to the new DataTable.

The following is the calling convention for the SelectGroupByInto method: dt = dsHelper.SelectInto(&quot;OrderSummary&quot;, ds.Tables!Employees, &quot;EmployeeID,sum(Amount) Total,min(Amount) Min,max(Amount) Max&quot;, &quot;EmployeeID<5&quot;, &quot;EmployeeID&quot;) This call sample creates a new DataTable with a TableName of OrderSummary and four fields (EmployeeID, Total, Min, and Max). These four fields have the same data type as the EmployeeID and the Amount fields in the Orders table. Then this sample reads records from the Orders DataTable and writes records to the OrderSummary DataTable. The OrderSummary DataTable contains the EmployeeID field and three different aggregates of the Amount field that are filtered on &quot;EmployeeID<5&quot; and that are grouped on (and sorted by) EmployeeID. If the GroupBy argument is blank, the target DataTable contains only a single record that aggregates all the input.

Note The filter expression is applied before any aggregate functionality. To implement HAVING-type functionality, filter the DataTable that results.

To call the SelectGroupByInto method, add the following method to the DataSetHelper class that you created in the &quot;DataSetHelper Shell Class&quot; section: Public Function SelectGroupByInto(ByVal TableName As String, _                                 ByVal SourceTable As DataTable, _                                  ByVal FieldList As String, _                                  Optional ByVal RowFilter As String = &quot;&quot;, _                                  Optional ByVal GroupBy As String = &quot;&quot;, _                                  Optional ByVal Rollup As Boolean = False) As DataTable '   ' Selects data from one DataTable to another and performs various aggregate functions ' along the way. See InsertGroupByInto and ParseGroupByFieldList for supported aggregate functions. '   Dim dt As DataTable = CreateGroupByTable(TableName, SourceTable, FieldList) InsertGroupByInto(dt, SourceTable, FieldList, RowFilter, GroupBy, Rollup) Return dt End Function back to the top

Test the Application
<ol> Save and then compile the DataSetHelper class that you created in the previous sections.</li> Follow these steps to create a new Visual Basic Windows Application: <ol style="list-style-type: lower-alpha;"> Start Visual Studio .NET.</li> On the File menu, point to New, and then click Project.</li> In the New Project dialog box, click Visual Basic Projects under Project Types, and then click Windows Application under Templates.</li></ol> </li> In Solution Explorer, right-click the solution, and then click Add Existing Project. Add the DataSetHelper project.</li> On the Project menu, click Add Reference.</li> In the Add Reference dialog box, click the Projects tab, and then add a reference to the DataSetHelper project to the Windows Form application.</li> In the form designer, drag three Button controls and a DataGrid control from the toolbox to the form. Name the buttons btnCreateGroupBy, btnInsertGroupByInto , and btnSelectGroupByInto. Keep the default name for the DataGrid control (DataGrid1).</li>  In the form code, add the following Imports statement to the top of the code window: Imports System.Data </li>  Add the following variable declarations to the form definition: Dim ds As DataSet, dsHelper As DataSetHelper.DataSetHelper </li>  Add the following code to the Form.Load event: ds = New DataSet dsHelper = New DataSetHelper.DataSetHelper(ds) ' ' Create source table ' Dim dt As New DataTable(&quot;Orders&quot;) dt.Columns.Add(&quot;EmployeeID&quot;, GetType(String)) dt.Columns.Add(&quot;OrderID&quot;, GetType(Integer)) dt.Columns.Add(&quot;Amount&quot;, GetType(Decimal)) dt.Rows.Add(New Object {&quot;Sam&quot;, 5, 25.00}) dt.Rows.Add(New Object {&quot;Tom&quot;, 7, 50.00}) dt.Rows.Add(New Object {&quot;Sue&quot;, 9, 11.00}) dt.Rows.Add(New Object {&quot;Tom&quot;, 12, 7.00}) dt.Rows.Add(New Object {&quot;Sam&quot;, 14, 512.00}) dt.Rows.Add(New Object {&quot;Sue&quot;, 15, 17.00}) dt.Rows.Add(New Object {&quot;Sue&quot;, 22, 2.50}) dt.Rows.Add(New Object {&quot;Tom&quot;, 24, 3.00}) dt.Rows.Add(New Object {&quot;Tom&quot;, 33, 78.75}) ds.Tables.Add(dt) </li> <li> Add the following code to the btnCreateGroupBy.Click event: Try dsHelper.CreateGroupByTable(&quot;OrderSummary&quot;, ds.Tables!Orders, &quot;EmployeeID,count(EmployeeID) Orders,sum(Amount) OrderTotal,max(Amount) BestOrder,min(Amount) WorstOrder&quot;) DataGrid1.SetDataBinding(ds, &quot;OrderSummary&quot;) Catch ex As Exception MsgBox(&quot;An Error Occured: &quot; & vbCrLf & ex.Message) End Try </li> <li> Add the following code to the btnInsertGroupByInto.Click event: Try dsHelper.InsertGroupByInto(ds.Tables!OrderSummary, ds.Tables!Orders, &quot;EmployeeID,count(EmployeeID) Orders,sum(Amount) OrderTotal,max(Amount) BestOrder,min(Amount) WorstOrder&quot;, &quot;&quot;, &quot;EmployeeID&quot;) DataGrid1.SetDataBinding(ds, &quot;OrderSummary&quot;) Catch ex As Exception MsgBox(&quot;An Error Occured: &quot; & vbCrLf & ex.Message) End Try </li> <li> Add the following code to the btnSelectGroupByInto.Click event. This sample sets the Rollup argument to TRUE to produce a Grand Total line and also totals for each employee: Try dsHelper.SelectGroupByInto(&quot;OrderSummary2&quot;, ds.Tables!Orders, &quot;EmployeeID,count(EmployeeID) Orders,sum(Amount) OrderTotal,max(Amount) BestOrder,min(Amount) WorstOrder&quot;, &quot;OrderID>10&quot;, &quot;EmployeeID&quot;, True) DataGrid1.SetDataBinding(ds, &quot;OrderSummary2&quot;) Catch ex As Exception MsgBox(&quot;An Error Occured: &quot; & vbCrLf & ex.Message) End Try </li> <li>Run the application, and then click each of the buttons. Notice that the DataGrid is populated with the tables and the data from the code.

Note You can only click the btnCreateGroupBy and the btnSelectGroupByInto buttons one time. If you click either of these buttons more than one time, you receive an error message that you are trying to add the same table two times. Additionally, you must click btnCreateGroupBy before you click btnInsertGroupByInto; otherwise, the destination DataTable is not created. If you click the btnInsertGroupByInto button multiple times, you populate the DataGrid with duplicate records.</li></ol>

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Enhancement Ideas

 * The ColumnName and the DataType properties are the only properties that are copied to the destination DataTable. You can extend the CreateTable method to copy additional properties, such as the MaxLength property, or you can create new key columns.
 * You can expand the functionality so that you can specify fields from related DataTable objects.
 * You can expand the functionality by adding support for additional aggregate functions, such as the AVG or the STDEV function. If you do this, you must have dynamically created variables to track intermediate values. To track intermediate values, you can add member variables to the FieldInfo class, and then use those member variables to store intermediate values.

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Troubleshooting

 * The fieldname and the alias parts of the field list must comply with DataColumn naming conventions. The parser also restricts the names, in that the name must not contain a period (.), a comma, or a space.
 * If you click a button more than one time, the same table is added two times to the DataSet. This results in an exception. To work around this problem, you can add code to the test application to check whether a DataTable of the same name already exists. Alternatively, you can create the DataSetHelper class without a reference to a DataSet and then bind the DataGrid.DataSource property directly to the dt variable instead of by using the SetDataBinding method call.
 * If the source table uses custom data types (for example, a class), you must add code to the InsertGroupByInto method to perform a deep copy of the data. Otherwise, only a reference is copied.

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Keywords: kbhowtomaster kbsystemdata KB325685

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