如果你不在乎每个order_no你得到哪一行，也许最简单的解决方案（Oracle 12之前）是：

 选择[无论你想要的列，可能不是rn  - 见下文] 
从（select order_table。*，
 row_number（）over（partition by order_no order by null）as rn 
）
其中rn = 1 
; 
 

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 what I want is to keep only one row for each order_no (no matter which one it is)

Is anyone knows how to do this? (FYI, I am using Oracle 10)

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
;