On Thu, Jul 23, 2009 at 3:24 PM, Michael Bayer<[email protected]> wrote:
> im assuming you're using MySQL since the GROUP BY below doesn't
> accommodate every column in the subquery (would be rejected by most DBs).
Corrected. It was Sqlite, but good catch.
> youll want to query each column individually that is part of what you are
> grouping by. i think you also need to use func.max() here and not
> func.min().
Yes, dumbpants on me there!
the join of the subquery to parent table is then probably
> just on hop_id. no "correlation" of subquery is needed either since you
> are intersecting two complete sets together (all routes intersected with
> all "max hop id" routes grouped by x, y, z).
>
How do I implement this join? If I do this:
sq =
session.query(Route.ts,Route.startpoint,Route.target,func.max(Route.hop_id).label('max_hop'))
sq = sq.group_by(Route.ts,Route.startpoint,Route.target).subquery()
then:
q = session.Query(Route,*sq.c).join(???)
What would that join be on? Hop_id isn't in the subquery.
I don't mean to be dense, but I'm not quite getting your response.
Perhaps I don't understand what correlated subqueries in SqlA are.
Is there is a reference that explains where they're used?
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