Regrouper des lignes en une seule

Bonjour, j'ai un problème avec une requête SQL, je souhaite regrouper plusieurs lignes en 1 seules avec un SUM.
Voici la requête SQL je vous passe le

FROM

et le

Where

:

SELECT comptet.CT_Classement AS CLIENT
 ,docligne.ar_ref as REFERENCE_ARTICLE
 ,DL_Design as DESIGNATION_ARTICLE
 ,(CASE WHEN convert(date,convert(varchar(10),DO_DateLivr,103)) < convert(date,convert(varchar(10),CURRENT_TIMESTAMP,103)) then (
  --datepart(week, DO_DateLivr) < datepart(week, CURRENT_TIMESTAMP) and year(DO_DateLivr) <= year(CURRENT_TIMESTAMP)
   case when year(DO_DateLivr) < year(CURRENT_TIMESTAMP) then SUM(convert(int,docligne.DL_QteBC))  else (
    case when DATEPART(week, DO_DateLivr) < datepart(week, CURRENT_TIMESTAMP) then SUM(convert(int,docligne.DL_QteBC)) else 0 end
   ) end
  ) else 0 end) as QUANTITE

 ,(CASE WHEN convert(date,convert(varchar(10),DO_DateLivr,103)) < convert(date,convert(varchar(10),CURRENT_TIMESTAMP,103)) then (
  --datepart(week, DO_DateLivr) < datepart(week, CURRENT_TIMESTAMP) and year(DO_DateLivr) <= year(CURRENT_TIMESTAMP)
   case when year(DO_DateLivr) < year(CURRENT_TIMESTAMP) then SUM(docligne.DL_MontantHT)  else (
    case when DATEPART(week, DO_DateLivr) < datepart(week, CURRENT_TIMESTAMP) then SUM(docligne.DL_MontantHT) else 0 end
   ) end
  ) else 0 end) as prix

 ,CONVERT(date,convert(varchar(10),date_livraison.min_date,103)) as DATE
from ...
where ...

group by 
comptet.CT_Classement
,docligne.AR_Ref
,min_date
,DL_Design
,DO_DateLivr

Pour l'instant j'ai:
client article quantité prix date
client1 a1 2 50 2021/02/01
client1 a1 4 100 2021/02/01

Je souhaite
client article quantité prix date
client1 a1 6 150 2021/02/01.

Merci de votre aide.

PS: je suis sur SQL SERVER 2019