; WITH cteTableName AS
(
	SELECT	ROW_NUMBER() OVER( PARTITION BY Man_name ORDER BY Model ) RowNum, *
	FROM	TableName
)

SELECT	CASE WHEN RowNum > 1 THEN '' ELSE Man_name END Man_name, Model
FROM	cteTableName

use tempdb
go

declare @tbl table (id int not null primary key, vc varchar(10))

insert into @tbl (id, vc)
select 1, 'aaa'
union
select 2, 'bbb'
union
select 3, 'aaa'
union
select 4, 'aaa'
union
select 5, 'ccc';


with NotToUpdate as(
	select MIN(id) as id, vc
	from @tbl
	group by vc)
update t
set t.vc = ''
from @tbl t left join NotToUpdate NTU on t.id = NTU.id
where NTU.id is null

select * from @tbl