declare @t table (ID varchar(3),CUSTOMER varchar(3),PRODUCTNUMBER varchar(6))
insert into @t
select '001','C01','P00001' union all
select '002','C01','P00001' union all
select '003','C02','P00002' union all
select '004','C02','P00002'

select * from @t t where
ID =(select min(ID) from @t where PRODUCTNUMBER=t.PRODUCTNUMBER)

/*
ID   CUSTOMER PRODUCTNUMBER
---- -------- -------------
001  C01      P00001
003  C02      P00002
*/

------解决方案--------------------
SQL code
select * from tb t where not exists(select 1 from tb
where CUSTOMER=t.CUSTOMER and PRODUCTNUMBER=t.PRODUCTNUMBER and id<t.id)

------解决方案--------------------
SQL code

select *
from tb t
where not exists (select 1 from tb where customer = t.customer and id > t.id)

------解决方案--------------------
+1
探讨

SQL code

select *
from tb t
where not exists (select 1 from tb where customer = t.customer and id > t.id)


------解决方案--------------------
探讨

ID CUSTOMER PRODUCTNUMBER
001 C01 P00001
002 C01 P00001
003 C02 P00002
004 C02 P00002
005 C03 P00003
006 C04 P00004
 -------------------------
 结果：
ID CUSTOMER PRODUCTNUMBER
001 C01 P00001
……


------解决方案--------------------
SQL code

select *
from tb t
where not exists (select 1 from tb where customer = t.customer and id > t.id)
  and exists (select 1 from tb where customer = t.customer and id <> t.id)

------解决方案--------------------
SQL code

use tempdb;
/*
create table A
(
    ID nvarchar(10) not null,
    CUSTOMER nvarchar(10) not null,
    PRODUCTNUMBER nvarchar(10) not null
);
insert into A values
('001','C01','P00001'),
('002','C01','P00001'),
('003','C02','P00002'),
('004','C02','P00002'),
('005','C03','P00003'),
('006','C04','P00004');
*/
select B.ID,B.CUSTOMER,B.PRODUCTNUMBER
from
(
    select *,row_number() over(partition by A.CUSTOMER,A.PRODUCTNUMBER order by A.ID desc) as [orderno] from A
) as B
where B.[orderno] = 1;

------解决方案--------------------
SQL code
declare @t table (ID varchar(3),CUSTOMER varchar(3),PRODUCTNUMBER varchar(6))
insert into @t
select '001','C01','P00001' union all
select '002','C01','P00001' union all
select '003','C02','P00002' union all
select '004','C02','P00002' union all
select '005','C03','P00003' union all
select '006','C04','P00004'

SELECT MIN(ID) FROM @T GROUP BY PRODUCTNUMBER HAVING COUNT(1)>1