Find duplicates and remove uplidates

From the internet:

1) Delete duplicates

delete from t
where rowid in (
                 select rid

                 from ( select rowid rid, row_number() over (partition by cust_seg_nbr order by rowid) rn
                              from t
                           )
                  where rn <> 1 )

2) Find how many duplicates

select cust_seg_nbr, count(*) from t group by cust_seg_nbr