Working out Duplicated Data in a Customer Data Base
Here are your duplicates, then everything else is your non-duplicate.

with c as (
    select *,
    row_number() over (partition by PostSur, Name  order by ID) as rowID 
    from Aron_Reporting.dbo.Customer_NewSort
)
select c.*
    from c 
    inner join c c2 on c.PostSur = c2.PostSur AND c.rowID &gt; 1 AND c2.rowID = 1 as rowID
     order by PostSur


This code partitions the row numbers by PostSur but also name, that way every person with a different name, or PostSur starts the numbering over. I joined the results back to the anchor, but you really don't need that necessarily.

I think I understood your requirements, hopefully this at least gets you close.