БД книжный магазин

Private Sub kol_BeforeUpdate(Cancel As Integer)
    Dim s, n
    s = "SELECT book.id_book, nz(Max(book.kolichestvo),0) as Kol, nz(Sum(zakazpodch.kol),0) AS SumProd " _
    & "FROM book INNER JOIN zakazpodch ON book.id_book = zakazpodch.id_book " _
    & "where zakazpodch.id_book=" & Me.id_book _
    & " GROUP BY book.id_book "
    With CurrentDb.OpenRecordset(s)
        If Val(!SumProd) + Me.kol >= Val(!kol) Then
            MsgBox "осталось всего " & !kol - !SumProd & " книг " & Me.id_book.Column(1)
            Cancel = True
        End If
    End With
End Sub

Private Sub Кнопка15_Click()
    DoCmd.OpenReport "Копия чек", acViewPreview, , "zakaz_id_zakaz=" & Me.id_zakaz
End Sub

Private Sub btnClear_Click()
    Dim i
    Me.Poisk = Null
    For i = 1 To 6
        If i <> 5 Then Me("Poisk" & i) = Null
    Next
    Me.Поле22 = Null
    Me.Поле24 = Null
    Me.Filter = ""
    Me.FilterOn = False
End Sub