Try This
select T1. Dscription,T1.docEntry,T1.Quantity,T1.Price ,
(select isnull(T2.LineText,'') from QUT10 t2 where t2.DocEntry=t0.docentry and and t1.linenum=t2.aftlinenum) as Ltext
from OQUT T0 INNER JOIN QUT1 T1 ON T0.DocEntry = T1.DocEntry
where T1.DocEntry='590'