Remove duplicate rows in a table

Question

I have a table contains order information like below:

Order table:

As we can see from that table, each order_no has several duplicates. So

Answer 1

If you don't care which row you get for each order_no, perhaps the simplest solution (before Oracle 12) is:

select [whatever columns you want, probably not rn - see below]
from ( select order_table.*,
              row_number() over (partition by order_no order by null) as rn
     )
where rn = 1
;