create table bs(value varchar(1))

insert into bs
select 'a' union all
select 'b' union all
select 'b' union all
select 'c' union all
select 'c' union all
select 'c'

select value from bs

value
-----
a
b
b
c
c
c


-- 执行一次操作后，表变成{b,c,c}
;with t as
( select row_number() over(partition by value order by (select 0)) rn
  from bs
)
delete from t where rn=1

select value from bs 

value
-----
b
c
c


-- 再执行一次，变成{c}
;with t as
( select row_number() over(partition by value order by (select 0)) rn
  from bs
)
delete from t where rn=1

select value from bs 

value
-----
c