how to get a Row with Max value of a column?

Question

My table is like

  P_ID  |  NAME  | SRNO | Rate 
    1   |   PR1  |  1   |  50  
    1   |   PR1  |  2   |  60  
    1   |   PR1  |  3   |  80  ----
    2   |   PR2  |  1   |  10 
    2   |   PR2  |  2   |  20  ----
    3   |   PR3  |  1   |  70  ----
    4   |   PR4  |  1   |  25 
    4   |   PR4  |  2   |  35  ----

I want to details whose SrNo is Maximum for each product.
Like this :

  P_ID  |  NAME  | SRNO | Rate 
    1   |   PR1  |  3   |  80
    2   |   PR2  |  2   |  20
    3   |   PR3  |  1   |  70
    4   |   PR4  |  2   |  35

How shall I do it???

Answer 1

You can use a correlated subquery:

select t.*
from mytable t
where t.srno = (select max(srno) from mytable t1 where t1.p_id = t.p_id)

With an index on (p_id, srno), this should be an efficient solution.

Anoter common solution is to use row_number():

select pid, name, srno, rate
from (
    select t.*, row_number() over(partition by p_id order by srno desc) rn
    from mytable t
) t
where rn = 1