How do you define which record is the second record? When you have 2 values do you have a rule that according to it you know which one to update and which record to leave as it is? Assuming that you do it by a key, here is a small example of how to do it:

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

Adi