SQLAlchemy: show only latest result if a join returns multiple results

Question

I\'m trying to create a Flask app that shows the latest score from individual players. So a player can have multiple scores, but on the leaderboard I only want to show her m

Answer 1

You can use the DISTINCT ON ... ORDER BY "idiom" in Postgresql to get the greatest-n-per-group, where n equals 1, given that your table isn't huge:

players_with_score = db.session.query(Player, Score).\
    join(Score).\
    distinct(Player.id).\
    order_by(Player.id, Score.timestamp.desc())

Since Score.timestamp is not nullable, you do not need to worry about descending order and NULLs.