>I think the most simplified way to do this and it seems to work ok is like this:
>
>

>SELECT 
>   (SELECT TOP 1 Invoice.ApprovedPersonName FROM Invoice WHERE Invoice.NoClient=Client.Numero ORDER BY Invoice.AddDate) AS FirstPerson,
>   (SELECT TOP 1 Invoice.ApprovedPersonName FROM Invoice WHERE Invoice.NoClient=Client.Numero ORDER BY Invoice.AddDate DESC) AS LastPerson
>

Just to fully understand your requirements: do you want to retrieve FirstPerson and LastPerson for each one of Client.Numero or just for an specific one that is set somewhere else in your application?