select * from V$VERSION;

create table test_table(unmask varchar(20), mask varchar(20));

insert into test_table values('123', '897609');

insert into test_table values('00123','896509');

insert into test_table values('0000456','5632789');

insert into test_table values('456','32567889');

insert into test_table values('5678','5632789');

select * from test_table;

select cast(unmask as number) as unmask_num, unmask, mask from test_table;

with duplicates as ( select cast(unmask as number) as unmask_num, count(*) as cnt from test_table group by cast(unmask as number) ) select * from duplicates join test_table on duplicates.unmask_num = cast(unmask as number) where cnt>1;

with duplicates as ( select cast(unmask as number) as unmask_num, count(*) as cnt from test_table group by cast(unmask as number) having count(*)>1 ) select * from duplicates join test_table on duplicates.unmask_num = cast(unmask as number) ;