批量更新 mysql 表并从 datagridview 计算值。VB.NET

我想使用datagridview中的值批量更新我的数据库表，但我还需要先求datagridview和mysql表的值之和。我该怎么做？

这是我的更新按钮的当前代码

        For Each row As DataGridViewRow In dgvStok.Rows
            If (Not row.IsNewRow) Then
                Dim ID As DataGridViewCell = row.Cells("ID").Value
                Dim Stok As DataGridViewCell = row.Cells("Stok").Value

                conn = New MySqlConnection('myconnstring)
                conn.Open()

                cmd = New MySqlCommand("Select * from tbStok where ID='" & ID & "'", conn)
                dr = cmd.ExecuteReader
                dr.Read()
                If dr.HasRows Then
                    Dim StokInventory, IncomingStok As Integer
                    StokInventory = dr.Item("Stok")
                    TotalStok = StokInventory + IncomingStok

                    Dim updateStok As String = "update tbStok set Stok ='" & TotalStok & "' where ID = '" & ID & "'"
                    cmd = New MySqlCommand(updateStok, conn)
                    cmd.ExecuteNonQuery()
                End If
                conn.Close()
            End If
        Next