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create table t (Rownumber int,OldIdassigned varchar(100),commoncode varchar(100));
 hidden batch(es)

insert into t values(1,'FLEX','Y2573F102'), (2,'RCL','Y2573F102'),(3,'FLEX','Y2573F102'), (4,'QGEN','N72482123'),(5,'QGEN','N72482123'), (6,'QGEN','N72482123'),(7,'RACE','N72482123'), (8,'CLB','N22717107'),(9,'CLB','N22717107'), (10,'CLB','N22717107')
10 rows affected
 hidden batch(es)

delete t2 from (select t1.*, row_number() over(partition by commoncode,OldIdassigned order by Rownumber) rn from t t1 )t2 where rn<>1 ;
5 rows affected
 hidden batch(es)

select * from t
Rownumber OldIdassigned commoncode
1 FLEX Y2573F102
2 RCL Y2573F102
4 QGEN N72482123
7 RACE N72482123
8 CLB N22717107
 hidden batch(es)