how to select only row with max sequence without using a subquery?

Question

I\'m trying to select only the row with the highest seq for each ID

ID  |  Seq   |  Age
-------------------
 A      1       20   
 A      2       30
 B               


        

Answer 1

Assuming SQL-Server ( >= 2005) or Oracle (10g?):

WITH CTE AS
( 
   SELECT
       ROW_NUMBER() OVER (PARTITION BY ID  ORDER BY Seq DESC) AS RN
       , ID, Age
   FROM 
       Persons
)
SELECT ID, Age 
FROM CTE
WHERE RN = 1

ROW_NUMBER returns the sequential number of a row within a partition of a result set.

Edit: works also in Oracle as you can see here: http://sqlfiddle.com/#!4/b7e79/2/0

Answer 2

In general, you neeed to use windowing or ranking functions - Rank(), Row_number(), etc.

select *
from
(
    select *, row_number() over (partition by id order by age desc) rn
    from yourtable
) v
where rn = 1

This will work in SQL Server 2005+ - in oracle you may need to specify the field names explicitly, instead of the *

Answer 3

Just in case you use an RDBMS that doesn't support window functions, you can use:

SELECT  Persons.ID, Persons.Age, Persons.Seq
FROM    Persons
        INNER JOIN
        (   SELECT  Persons.ID, MAX(Seq) AS Seq
            FROM    Persons
            GROUP BY Persons.ID
        ) MaxP
            ON MaxP.ID = Persons.ID
            AND MaxP.Seq = Persons.Seq

It still involves a subquery, but I don't see a way of doing this without one, nor do I really understand why you would want to avoid them.