sql fetch one record per date from table

Question

I have a table like:

o_id  order_no   date        etc....
 4     1         2017-02-01
 4     2         2017-02-01
 4     3         2017-02-01

what i want is only one(highest order no) record per date should be fetched. For example for only order_no 3 for o_id 4 should be fetched

Output:

o_id       order_no      date
4          3             2017-02-01
2          1             .........so on

Answer 1

The canonical method is to use the ANSI-standard ROW_NUMBER() function:

select t.*
from (select t.*,
             row_number() over (partition by o_id order by order_no desc) as seqnum
      from t
     ) t
where seqnum = 1;

Answer 2

You may use GROUP BY and MAX if the order_no is unique in each o_id group

select your_table.*
from your_table
join
(
  select o_id, max(order_no) maxorder
  from your_table
  group by o_id
) t on t.o_id = your_table.oid and t.maxorder = your_table.order_no

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