Python 如何建立一种混合的方法来计算过去X天的记录数？

我有一个乒乓球比赛表，我想创建一个查询字段，统计焦点比赛日期范围内的前几场比赛的数量。例如：

+----------+------------+---------------------------+
| match_id |    date    | num_matches within 3 days |
+----------+------------+---------------------------+
|        1 | 01/01/2020 |                         0 |
|        2 | 02/01/2020 |                         1 |
|        3 | 03/01/2020 |                         2 |
|        4 | 05/01/2020 |                         2 |
|        5 | 05/01/2020 |                         3 |
|        6 | 10/01/2020 |                         0 |
+----------+------------+---------------------------+

我已尝试使用所述的相关子查询，但我不知道如何创建条件：

@hybrid_method
def match_count(self, timespan_days):
    cut_off = self.date_time_inferred - timedelta(days=timespan_days)
    return sum(x >= cut_off and <some_cond_for_less_than_current_match_date> for x in self.date_time_inferred)

@match_count.expression
def match_count(cls, timespan_days):
    cut_off = cls.date_time_inferred - timedelta(days=timespan_days)
    return (
        select(func.count(cls.date_time_inferred)).
        where(
            and_(
                cls.date_time_inferred.__ge__(cut_off),
                cls.date_time_inferred.__lt__(<not_sure_what_goes_here>),
            )
        ).label('match_count')
    )

关于守则：

select(func.count(cls.date))

所以我显然做错了一大堆事情

希望有人能帮助我了解如何解决这个问题？也非常愿意用不同的方式来完成同样的事情。我想继续使用混合属性…

下面是（几乎）完整的代码片段：

# ... omitted import statements and session configuration

def _date(date_str):
    return datetime.strptime(date_str, "%Y-%m-%d")


class Match(Base):
    __tablename__ = "match"

    match_id = Column(Integer, primary_key=True)
    date = Column(Date, nullable=False)

    @hybrid_method
    def match_count(self, timespan_days):
        cut_off = self.date - timedelta(days=timespan_days)
        sess = object_session(self)
        M = Match
        q = (
            sess.query(M)
            # .filter(M.match_id != self.match_id)  # option-1: only other on the same day
            .filter(M.match_id < self.match_id)  # option-2: only smaller-id on the same day (as in OP)
            .filter(M.date <= self.date)
            .filter(M.date >= cut_off)
        )
        return q.count()

    @match_count.expression
    def match_count(cls, timespan_days):
        M = aliased(Match, name="other")
        cut_off = cls.date - timespan_days
        q = (
            select([func.count(M.match_id)])
            # .filter(Match.match_id != self.match_id)  # option-1: only other on the same day
            .where(M.match_id < cls.match_id)  # option-2: only smaller-id on the same day (as in OP)
            .where(M.date <= cls.date)
            .where(M.date >= cut_off)
        )
        return q.label("match_count")


def test():
    Base.metadata.drop_all()
    Base.metadata.create_all()

    from sys import version_info as py_version
    from sqlalchemy import __version__ as sa_version

    print(f"PY version={py_version}")
    print(f"SA version={sa_version}")
    print(f"SA engine={engine.name}")
    print("=" * 80)

    # 1. test data
    matches = [
        Match(date=_date("2020-01-01")),
        Match(date=_date("2020-01-02")),
        Match(date=_date("2020-01-03")),
        Match(date=_date("2020-01-05")),
        Match(date=_date("2020-01-05")),
        Match(date=_date("2020-01-10")),
    ]
    session.add_all(matches)
    session.commit()
    print("=" * 80)

    # 2. test query in "in-memory"
    for m in session.query(Match):
        print(m, m.match_count(3))
    print("=" * 80)

    # 3. test query on "SQL"
    session.expunge_all()
    q = session.query(Match, Match.match_count(3))
    for match, match_count in q:
        print(match, match_count)
    print("=" * 80)


if __name__ == "__main__":
    test()

---

我想指出的一点是，“内存”检查不是很有效，因为必须为每个

Match

实例查询数据库。因此，如果可能，我将使用最后一个查询。

您的链接指向1.4文档。您是否正在使用1.4（目前处于测试阶段）？如果没有，请使用您正在使用的版本的文档：1.4包含重大更改。我正在使用1.3-感谢提醒-将更正链接。看起来相关子查询在1.3和1.4中都是相同的。如果仔细观察，你会发现它在1.4中是

select（…）

，但在1.3中是

select（[…]）

（因此你会看到错误消息）。啊！这就解决了我问题的第一部分——谢谢：）有什么关于如何处理我自己陷入的困境的提示吗？我不知道如何找到当前匹配的日期，所以我可以写一个小于条件…啊，当然-使用别名并计算：）非常感谢！明天我们会测试这个！嘿我一直在努力解决这个问题。在sess=object\u session（self）中调用的

object\u session

方法是什么？这大概是为了执行查询而创建

会话的一种方法吧？我通常有一个数据访问层类来创建
会话
，我使用它来生成查询。现在我从一个表类中查询，我将如何做不同的事情？遇到上述问题。将此作为一个新问题发布，因为我的直觉是，这可能是MySQL与PostgreSQL之间的问题……我发现了什么是
object\u session
。对于其他阅读本文的人-
# ... omitted import statements and session configuration

def _date(date_str):
    return datetime.strptime(date_str, "%Y-%m-%d")


class Match(Base):
    __tablename__ = "match"

    match_id = Column(Integer, primary_key=True)
    date = Column(Date, nullable=False)

    @hybrid_method
    def match_count(self, timespan_days):
        cut_off = self.date - timedelta(days=timespan_days)
        sess = object_session(self)
        M = Match
        q = (
            sess.query(M)
            # .filter(M.match_id != self.match_id)  # option-1: only other on the same day
            .filter(M.match_id < self.match_id)  # option-2: only smaller-id on the same day (as in OP)
            .filter(M.date <= self.date)
            .filter(M.date >= cut_off)
        )
        return q.count()

    @match_count.expression
    def match_count(cls, timespan_days):
        M = aliased(Match, name="other")
        cut_off = cls.date - timespan_days
        q = (
            select([func.count(M.match_id)])
            # .filter(Match.match_id != self.match_id)  # option-1: only other on the same day
            .where(M.match_id < cls.match_id)  # option-2: only smaller-id on the same day (as in OP)
            .where(M.date <= cls.date)
            .where(M.date >= cut_off)
        )
        return q.label("match_count")


def test():
    Base.metadata.drop_all()
    Base.metadata.create_all()

    from sys import version_info as py_version
    from sqlalchemy import __version__ as sa_version

    print(f"PY version={py_version}")
    print(f"SA version={sa_version}")
    print(f"SA engine={engine.name}")
    print("=" * 80)

    # 1. test data
    matches = [
        Match(date=_date("2020-01-01")),
        Match(date=_date("2020-01-02")),
        Match(date=_date("2020-01-03")),
        Match(date=_date("2020-01-05")),
        Match(date=_date("2020-01-05")),
        Match(date=_date("2020-01-10")),
    ]
    session.add_all(matches)
    session.commit()
    print("=" * 80)

    # 2. test query in "in-memory"
    for m in session.query(Match):
        print(m, m.match_count(3))
    print("=" * 80)

    # 3. test query on "SQL"
    session.expunge_all()
    q = session.query(Match, Match.match_count(3))
    for match, match_count in q:
        print(match, match_count)
    print("=" * 80)


if __name__ == "__main__":
    test()

============================================================
PY version=sys.version_info(major=3, minor=8, micro=1, releaselevel='final', serial=0)
SA version=1.3.20
SA engine=postgresql
============================================================
<Match(date=datetime.date(2020, 1, 1), match_id=1)> 0
<Match(date=datetime.date(2020, 1, 2), match_id=2)> 1
<Match(date=datetime.date(2020, 1, 3), match_id=3)> 2
<Match(date=datetime.date(2020, 1, 5), match_id=4)> 2
<Match(date=datetime.date(2020, 1, 5), match_id=5)> 3
<Match(date=datetime.date(2020, 1, 10), match_id=6)> 0
============================================================
<Match(date=datetime.date(2020, 1, 1), match_id=1)> 0
<Match(date=datetime.date(2020, 1, 2), match_id=2)> 1
<Match(date=datetime.date(2020, 1, 3), match_id=3)> 2
<Match(date=datetime.date(2020, 1, 5), match_id=4)> 2
<Match(date=datetime.date(2020, 1, 5), match_id=5)> 3
<Match(date=datetime.date(2020, 1, 10), match_id=6)> 0
============================================================

SELECT match.match_id,
       match.date,

  (SELECT count(other.match_id) AS count_1
   FROM match AS other
   WHERE other.match_id < match.match_id
     AND other.date <= match.date
     AND other.date >= match.date - %(date_1)s) AS match_count
FROM match