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      1       25
 B      2       32
 B      3       44
 B      4       48
 C      1       11

This appears to work

SELECT ID, Age
FROM Persons a
WHERE Seq = (SELECT MAX(Seq) FROM Persons b WHERE a.ID = b.ID)

But is this the best way, the only way? I don’t like using subqueries if I don’t have to and I recall you can use something but I forget what it is. Any idea?

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