Visual Basic.NET - Sumar Registros Duplicados en una Tabla en Visual Basic

Dim cmda As New OleDb.OleDbCommand

Dim Stotal As Double = 0

Dim cant As Double = 0

Dim punit As Double = 0

Dim fecha As String

Dim sqla As String

Dim ref, ref1 As Integer

cmd.Connection = conn

cmd.CommandType = CommandType.Text

cmd.CommandText = "SELECT CODITEM, ITEM, PRECIO, CANTIDAD, TOTALITEM, FECHA, REFERENCIA FROM MESAS WHERE MESA = " & mesa & ""

dr = cmd.ExecuteReader()

If dr.HasRows Then

    While dr.Read()

        producto = dr(0).ToString

        descripcion = dr(1).ToString

        punit = CDbl(dr(2))

        cant = 0

        Stotal = 0

        fecha = dr(5).ToString

        ref = Val(dr(6))

        cmdPG.Connection = conn

        cmdPG.CommandType = CommandType.Text

        cmdPG.CommandText = "SELECT CODITEM, ITEM, PRECIO, CANTIDAD, TOTALITEM, FECHA, REFERENCIA FROM MESAS WHERE MESA = " & mesa & " AND CODITEM = " & producto & ""

        drPG = cmdPG.ExecuteReader()

        If drPG.HasRows Then

            'borrar registros de mesa

            cmda.CommandType = CommandType.Text

            cmda.Connection = conn

            sqla = "DELETE FROM MESAS WHERE MESA = " & mesa & " AND REFERENCIA = " & ref1 & " "

            cmda.CommandText = sqla

            While drPG.Read()

                If producto = drPG(0).ToString Then

                    ref1 = Val(drPG(6))

                    cant = cant + CDbl(drPG(3))

                    If punit < CDbl(drPG(2)) Then

                        punit = CDbl(drPG(2))

                    End If

                End If

                'borra el registro leído

                If (ref1 <> ref) And (producto = dr(0).ToString) Then

                    MsgBox(ref.ToString + " y " + ref1.ToString)

                    cmda.ExecuteNonQuery()

                End If

            End While

        End If

        drPG.Close()

        Stotal = cant * punit

        ' Actualiza los valores

        sqla = "UPDATE MESAS SET "

        sqla += "PRECIO = " & Str(punit) & ", "

        sqla += "CANTIDAD = " & Str(cant) & ", "

        sqla += "TOTALITEM = " & Str(Stotal) & " "

        sqla += "WHERE MESA = " & mesa & " AND REFERENCIA = " & ref & " "

        cmda.CommandText = sqla

        cmda.ExecuteNonQuery()

    End While

Else

    MsgBox("No Existen Registros para la consulta")

End If

dr.Close()