Postgres select all columns but group by one column

Question

I have a simple table with a unit_id oid, time timestamp, diag bytea. The primary key is a combination of both time and unit_id.

The idea behind this query is to get the

Answer 1

You can join the grouped select with the original table:

SELECT d.time, d.diag, d.unit_id
FROM(
    SELECT unit_id, max(time) as max_time
    FROM diagnostics.unit_diag_history
    GROUP BY unit_id
) s JOIN diagnostics.unit_diag_history d
ON s.unit_id = d.unit_id AND s.max_time = d.time