Without knowing the structure of all your tables and data its difficult to help, this may point you in the right direction (untested as no consumable data):

SELECT

Qry.platenr

, 'invoicefm' AS Company

, Qry.ClientId

, Qry.Name

, Qry.Invoice_id AS Document_Nr

, Qry.Invoice_Date

, Qry.Paid, Qry AS AllValues

FROM

(

SELECT

*

,ROW_NUMBER() OVER (PARTITION BY Invoice_FM .DOCUMENT_NR ORDER BY vehicle .Platenr) AS RowNum

FROM

Invoice_FM

INNER JOIN Client

ON Invoice_FM.ClientId = Client.ClientID

LEFT JOIN vehicle

ON Invoice_FM.Invoice_id = vehicle.Invoice_Nr

WHERE Invoice_FM.deleted = 0

AND client.type_client = 'Fleet'

) AS Qry

WHERE

Qry.RowNum = 1

ORDER BY Document_Nr

Andy