Private Dateiname As String = _
      "c:\users\achim\desktop\rheinpegel\Test#1_W-N.csv"
    Private DbName As String = "c:\users\achim\desktop\rheinpegel\db1.mdb"
    Private Conn As New OleDbConnection("Provider=Microsoft.Jet.OLEDB.4.0;Data" _
      & _
      "Source=" & DbName)
    Private DA As New OleDbDataAdapter("SELECT * FROM Pegel;", Conn)
    Private CB As New OleDbCommandBuilder(DA)
    Private DT As New DataTable
 
    Private Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load
        Try
            Conn.Open()
            DA.Fill(DT)
            Conn.Close()
 
            DT.PrimaryKey = New DataColumn() {DT.Columns("Datum"), DT.Columns( _
              "Ort")}
            Grid1.DataSource = DT
        Catch ex As Exception
            MsgBox(ex.Message)
        End Try
    End Sub
 
    Private Sub btnStart_Click(sender As Object, e As EventArgs) Handles _
      btnStart.Click
        Dim dt2 As DataTable = CSV2Table(DT.Clone)
        DT.Merge(dt2, True)
 
        'Nur zur Überprüfung des Ergebnisses:
        Dim s As String = ""
        Dim DTt As DataTable
        DTt = DT.GetChanges(DataRowState.Unchanged) : If Not IsNothing(DTt) _
          Then s += "  Unv.: " & DTt.Rows.Count.ToString
        DTt = DT.GetChanges(DataRowState.Added) : If Not IsNothing(DTt) Then s _
        += "  Add.: " & DTt.Rows.Count.ToString
        DTt = DT.GetChanges(DataRowState.Modified) : If Not IsNothing(DTt) Then _
        s += "  Mod.: " & DTt.Rows.Count.ToString
        DTt = DT.GetChanges(DataRowState.Deleted) : If Not IsNothing(DTt) Then _
        s += "  Del.: " & DTt.Rows.Count.ToString
        MsgBox(s,, "Merged")
 
        Conn.Open()
        Dim i As Integer = DA.Update(DT)
        'Nur zur Überprüfung des Ergebnisses:
        MsgBox(i,, "Zurückgeschrieben")
        Conn.Close()
    End Sub
 
    Private Function CSV2Table(ByVal DT2 As DataTable) As DataTable
        :
        'In einer Schleife Datensätze (Anzahl > 3.000) einlesen
           DT2.Rows.Add({dDateTime, sOrt, iPegel})
 
        DT2.AcceptChanges()
        CSV2Table = DT2
    End Function