如何清除DataGridView

Question

当我使用包含主题代码的用户凭据登录以输入在DataGrid中为特定主题注册的学生的标记并保存到SQL Server数据库时，相同的标记为学生在登录时显示在DataGrid中的条目是使用不同的主题代码。

如果有人可以修改以下代码来解决问题，我将不胜感激。

Private Sub dgMarksEntry_Enter(ByVal sender As Object, ByVal e As System.EventArgs) Handles dgMarksEntry.Enter
    Try

        For i = 0 To dgMarksEntry.Rows.Count - 1
            cmd = New SqlCommand("select * from StudentDetails.MarksEntry where RegDNumber=" & Val(dgMarksEntry.Item(0, i).Value) & "  ", cn)

            dr = cmd.ExecuteReader
            If dr.Read Then
                dgMarksEntry.Item(2, i).Value = dr(1)
                dgMarksEntry.Item(3, i).Value = dr(2)
                dgMarksEntry.Item(4, i).Value = dr(3)
                dgMarksEntry.Item(5, i).Value = dr(4)
                dgMarksEntry.Item(6, i).Value = dr(5)
                dgMarksEntry.Item(7, i).Value = dr(6)
            End If
            dr.Close()
        Next
    Catch ex As Exception
        MessageBox.Show("MarksError:" & ex.Message)
    End Try