Can I use non-aggregate columns with group by?

Question

You cannot (should not) put non-aggregates in the SELECT line of a GROUP BY query.

I would however like access the one of the non-aggregate

Answer 1

In recent databases you can use sum() over (parition by ...) to solve this problem:

select id, kind, age as max_age from (
  select id, kind, age, max(age) over (partition by kind) as mage
    from table)
where age = mage

This can then be single pass