Try something like this:
; with Q as
(
select *,
row_number() over (partition by dep_id order by ID ) n
from emp_tbl
)
select
iif(n=1, cast(s.ID as varchar(max)), '') ID,
iif(n=1, cast(Q.dep_id as varchar(max)), '') emp_id,
Q.[name],
Q.[dept.],
iif(n=1, cast(s.[sal.] as varchar(max)), '') [sal.]
from Q
inner join sal_tbl s on s.emp_id = Q.dep_id
order by Q.ID, n