one_most_recent_by_group_query.sql

SELECT workouts.*
FROM workouts JOIN (
    SELECT max(id) AS id FROM (
        SELECT w.id, w.sport_id
        FROM workouts w JOIN (
            SELECT sport_id, max(created_at) AS created_at
            FROM workouts
            GROUP BY sport_id
        ) latest_by_sport
        ON w.created_at = w.created_at
        AND w.sport_id = latest_by_sport.sport_id
    ) all_most_recent_by_sport
    GROUP BY sport_id
) one_most_recent_by_sport
ON one_most_recent_by_sport.id = workouts.id