sqlalchemy join with sum and count of grouped rows

问题

Hi i am working on a little prediction game in flask with flask-sqlalchemy I have a User Model:

class User(db.Model, UserMixin):
    id = db.Column(db.Integer, primary_key=True)
    nick = db.Column(db.String(255), unique=True)
    bets = relationship('Bet', backref=backref("user"))

and my Bet model

class Bet(db.Model):
    id = db.Column(db.Integer, primary_key=True)
    uid = db.Column(db.Integer, db.ForeignKey('user.id'))
    matchid = db.Column(db.Integer, db.ForeignKey('match.id'))
    points = db.Column(db.Integer)

Both are not the full classes but it should do it for the question. A user can gather points for predicting the match outcome and gets different amount of points for predicting the exact outcome, the winner or the difference. I now want to have a list of the top users, where i have to sum up the points which i'm doing via

toplist = db.session.query(User.nick, func.sum(Bet.points)).\
    join(User.bets).group_by(Bet.uid).order_by(func.sum(Bet.points).desc()).all()

This works quite good, now there maybe the case that two players have the same sum of points. In this case the amount of correct predictions (rewarded with 3 points) would define the winner. I can get this list by

tophits = db.session.query(User.nick, func.count(Bet.points)).\
            join(User.bets).filter_by(points=3).all()

They both work well, but I think there has to be a way to get both querys together and get a table with username, points and "hitcount". I've done that before in SQL but i am not that familiar with SQLAlchemy and thought knots in my brain. How can I get both queries in one?

回答1:

In the query for tophits just replace the COUNT/filter_by construct with equivalent SUM(CASE(..)) without filter so that the WHERE clause for both is the same. The code below should do it:

total_points = func.sum(Bet.points).label("total_points")
total_hits = func.sum(case(value=Bet.points, whens={3: 1}, else_=0)).label("total_hits")
q = (session.query(
        User.nick,
        total_points,
        total_hits,
        )
    .join(User.bets)
    .group_by(User.nick)
    .order_by(total_points.desc())
    .order_by(total_hits.desc())
    )

Note that i changed a group_by clause to use the column which is in SELECT, as some database engines might complain otherwise. But you do not need to do it.

来源：https://stackoverflow.com/questions/21271382/sqlalchemy-join-with-sum-and-count-of-grouped-rows

标签

sql

sqlalchemy

flask-sqlalchemy