SQLAlchemy correlated subquery TypeError: Boolean value of this clause is not defined

Question

我需要编写一个 Python SQLAlchemy 代码来转换此 SQL 查询，但我找不到在 SQL Alchemy 中执行此查询的有意义的方法。

SELECT *
FROM alpha AS X
WHERE X.index = (
    SELECT
        MAX(index)
    FROM
        alpha AS Y
    WHERE
        X.question = Y.question
        AND X.person = Y.person
)

我试过这样，但我一直收到错误 TypeError: Boolean value of this clause is not defined（alpha 是 Table）。

from sqlalchemy.orm import aliased
from sqlalchemy import func, and_
X = aliased(alpha)
Y = aliased(alpha)
conn.execute(
    select(X).where(
        X.c.index
        == select(func.max(X.c.index))
        .where(
            and_(
                X.c.question == Y.c.question,
                X.c.person == Y.c.person,

            )
        )
        .correlate(X)
    )
)

我做错了什么？

Answer 1

我认为您真的只需要使用 scalar_subquery()。据我了解，关联会自动发生，如果 SQLAlchemy 无法分辨您的意思，您只需要 correlate。

代码

alpha = Table("alpha", metadata,
              Column("id", Integer, primary_key=True),
              Column("question", String),
              Column("person", String),
              Column("index", Integer),)



Base.metadata.create_all(engine)

with Session(engine) as session:
    X = aliased(alpha, name='X')
    Y = aliased(alpha, name='Y')

    q = select(X).where(
        X.c.index
        == select(func.max(X.c.index))
        .where(
            and_(
                X.c.question == Y.c.question,
                X.c.person == Y.c.person,

            )
        ).scalar_subquery()
    )
    print (q)

SQL

SELECT "X".id, "X".question, "X".person, "X".index 
FROM alpha AS "X" 
WHERE "X".index = (SELECT max("X".index) AS max_1 
FROM alpha AS "Y" 
WHERE "X".question = "Y".question AND "X".person = "Y".person)

这是使用 Postgresql 和 SQLAlchemy 1.4.31。

SQLAlchemy correlated subquery TypeError: Boolean value of this clause is not defined

SQLAlchemy correlated subquery TypeError: Boolean value of this clause is not defined

sql

orm

sqlalchemy

correlated-subquery

scalar-subquery

代码

SQL