用sqlalchemy汇总数据

Question

我要使用此表通过flask_sqlalchemy汇总烧瓶中的数据：

class User(db.Model, UserMixin):
    id = db.Column(db.Integer, primary_key=True)    
    pages= relationship('Page', backref=backref("user")) 
tags = db.Table('tags',
    db.Column('tag_id', db.Integer, db.ForeignKey('tag.id'), primary_key=True),
    db.Column('page_id', db.Integer, db.ForeignKey('page.id'), primary_key=True)
)

class Page(db.Model):
    id = db.Column(db.Integer, primary_key=True)
    name = db.Column(db.String(100))
    tags = db.relationship('Tag', secondary=tags, lazy='subquery',
        backref=db.backref('pages', lazy=True))

class Tag(db.Model):
    id = db.Column(db.Integer, primary_key=True)
    name = db.Column(db.String(100))

结果必须是这样的：

| user | count of pages | count of tags |
|------|----------------|---------------|
|      |                |               |