create table #tab (custno int not null,lineseqno int not null,value varchar(2))
insert into #tab values(2343,3,'DP')
insert into #tab values(2432,4,'VP')
insert into #tab values(2343,3,'IP')



DELETE a from  #tab a where  exists (select 1 from #tab where custno=a.custno and lineseqno=a.lineseqno ) and value<>(select top 1 value from #tab where custno=a.custno and lineseqno=a.lineseqno)

select * from #tab


alter table #tab add constraint pk_#tab primary key (custno,lineseqno)


custno      lineseqno   value
----------- ----------- -----
2343        3           DP
2432        4           VP

(2 行受影响)

delete a from tb a
where exists(select 1 from tb b where a.custno=b.custno and a.lineseqno=b.lineseqno and a.value<b.value)

select *  from service_number_extra a where  exists(select * from service_number_extra b  where a.custno=b.custno and  a.lineseqno=b.lineseqno 
group by custno,lineseqno
having count(1)>1)