Public Sub Sol01()

Dim ssq As String
ssq = ""
ssq = ssq & "SELECT  "
ssq = ssq & "tab1.Id, tab1.NumeroOrdine "
ssq = ssq & "FROM tab1 LEFT JOIN tab2 "
ssq = ssq & "ON tab1.NumeroOrdine = tab2.NumeroOrdine "
ssq = ssq & "WHERE (((tab2.NumeroOrdine) Is Null))"
ssq = ssq & ";"

Dim dbx As DAO.Database
Set dbx = DBEngine(0)(0)

Dim rsx As DAO.Recordset
Set rsx = dbx.OpenRecordset(ssq, dbOpenDynaset)

rsx.MoveFirst

    Do Until rsx.EOF
        MsgBox "Non Trovato id " & rsx.Fields("id") & "     numero ordine " & rsx.Fields("NumeroOrdine")
        rsx.MoveNext
    Loop

rsx.Close
dbx.Close
Set rsx = Nothing
Set dbx = Nothing

End Sub