Create table #works (ID_work int)
Create table #workdetail(ID_det int IDENTITY(1,1), ID_Work int,[Status] int default(0),comment varchar(max))
Create table #test (ID_wrk int, cmnt varchar(max))

insert into #works
select 1
union
select 2

insert into #workdetail (ID_Work,Status,comment)
select 1,1,'com1'
union
select 1,2,'com1-1'
union
select 2,0,'com2'
union
select 2,1,'com2-2'


insert into #test
select 1, 'new_com1'
union
select 2, 'new_com2'
union
select 3, ''

MERGE #workdetail AS d
USING (Select w.ID_work, d.ID_det, d.status, t.cmnt
		From #test t
		Inner Join #works w On t.ID_wrk=w.ID_work
		Inner Join #workdetail d On w.ID_work=d.ID_work 
		Where LEN(t.cmnt)>0
	) AS s
ON ( d.ID_det = s.ID_det and d.Status=0)
WHEN MATCHED  THEN
		UPDATE SET	d.Comment=s.cmnt
WHEN NOT MATCHED THEN
		INSERT (ID_work, Comment)
		VALUES (s.ID_work, s.cmnt);

with t as ( select w.ID_Work , w.ID_det, w.comment from  #workdetail w Inner Join #test t On w.ID_Work=t.ID_wrk where w.Status = 0 )
   , x as ( Select t.ID_wrk,  t.cmnt From #test t Where LEN(t.cmnt)>0 )
MERGE t using x ON  t.ID_Work=x.ID_wrk
WHEN MATCHED  THEN UPDATE SET Comment = x.cmnt
WHEN NOT MATCHED THEN INSERT (ID_work, Comment) VALUES(ID_wrk, cmnt);