BANK
SN    AMT
  1    100
  2    300
DELETE BANK B1 WHERE B1.ROWID<ANY
(SELECT B2.ROWID FROM BANK B2
WHERE B1.SN=B2.SN
AND B1.AMT=B2.AMT) ;

Above query doesn't work for NULLS.  Can you do something about it without evaluating NULLs to some value[NVL(AMT, 0)]

Solution by Arun :

Basically it depend on business logic.
For below sample problem we can use the script as:

truncate table bank

create table bank (SN number(2),amt number(8,2));

insert into bank values(1,100);
insert into bank values(1,100);
insert into bank values(1,100);
insert into bank values(2,200);
insert into bank values(2,200);
insert into bank values(2,200);
insert into bank values(null,null);
insert into bank values(null,null);
insert into bank values(null,null);
insert into bank values(1,null);
insert into bank values(1,null);
insert into bank values(null,400);
insert into bank values(null,400);

DELETE from BANK B1 WHERE B1.ROWID not in 
(SELECT min(B2.ROWID) FROM BANK B2 WHERE B1.SN=B2.SN AND B1.AMT=B2.AMT
union
SELECT min(B2.ROWID) FROM BANK B2 where B2.SN is null and B2.AMT is not null
union
SELECT min(B2.ROWID) FROM BANK B2 where B2.SN is not null and B2.AMT is null
union
SELECT min(B2.ROWID) FROM BANK B2 where B2.SN is null and B2.AMT is null
) ;

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