Update Third column if First Column has Duplicate values and Second column are Distinct with Comma delimiter:

create table #temp(ID int, ID2 Varchar(10),Results varchar(50))

insert into #temp values(1,'2',null)

insert into #temp values(1,'3',null)

insert into #temp values(1,'4',null)

insert into #temp values(2,'2',null)

insert into #temp values(2,'3',null)

insert into #temp values(2,'4',null)

insert into #temp values(2,'4',null)

insert into #temp values(3,'1',null)

insert into #temp values(4,'5',null)

insert into #temp values(5,'6',null)

insert into #temp values(5,'6',null)

select * from #temp

Execute below code:

;with cte

as

(

 select distinct t.ID,t.ID2,Results,

  STUFF((SELECT distinct ', ' + t1.ID2

         from #temp t1

         where t.[id] = t1.[id]

            FOR XML PATH(''), TYPE

            ).value('.', 'NVARCHAR(MAX)')

        ,1,2,'') department

from #temp t

)

Update t set t.Results=c.department from #temp t

inner join cte c

on t.ID=c.ID