อันนี้เป็น Code ที่ผมใช้ตรวจเชค เมื่อคลิกปุ่มขาย ก่อนตัดสต๊อก
Private Sub chkQty()
        Dim comSave As New SqlCommand
        Dim comUpdate As New SqlCommand
        Dim NumRows, i As Integer
        NumRows = grdOrder.Rows.Count - 1
        For i = 0 To NumRows

strSQL = "select * from Product WHERE(P_ID = '" & CStr((grdOrder.Rows(i).Cells(0).Value.ToString)) & "'
                                                    and stock < '" & CInt(grdOrder.Rows(i).Cells(3).Value) & "')"

            da = New SqlDataAdapter(strSQL, Conn)
            If IsFindchk = True Then
                ds.Tables("cQty").Clear()
                IsFindchk = False
                bQty = False
            End If
            da.Fill(ds, "cQty")
            If ds.Tables("cQty").Rows.Count <> 0 Then
                IsFindchk = True
                bQty = True
            End If
        Next
    End Sub