Db2 11.1

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create table t (a int not null, b int not null);
insert into t (a,b) values (1,1),(1,1),(1,1),(2,2),(3,3),(3,3);
select t.*, row_number() over (partition by a,b) as rn from t;


A
B
RN


1
1
1

1
1
2

1
1
3

2
2
1

3
3
1

3
3
2


delete from (
  select t.*, row_number() over (partition by a,b) as rn from t
) where rn > 1;  
select t.*, row_number() over (partition by a,b) as rn from t;


A
B
RN


1
1
1

2
2
1

3
3
1