Return row with the max value of one column per group [duplicate]

This is also possible without subquery:

SELECT DISTINCT
       id
      ,max(round) OVER (PARTITION BY id) AS round
      ,first_value(score) OVER (PARTITION BY id ORDER BY round DESC) AS score
FROM   SCORES
WHERE  id IN (1,2,3)
ORDER  BY id;

Returns exactly what you asked for.
The crucial point is that DISTINCT is applied after window functions.

SQL Fiddle.

Maybe faster because it uses the same window twice:

SELECT DISTINCT
       id
      ,first_value(round) OVER (PARTITION BY id ORDER BY round DESC) AS round
      ,first_value(score) OVER (PARTITION BY id ORDER BY round DESC) AS score
FROM   SCORES
WHERE  id IN (1,2,3)
ORDER  BY id;

Otherwise doing the same.