SQLAlchemy：使用子查詢和內部聯接從sql查詢創建sqlalchemy查詢

Question

我是后端開發和python的新手。 我正在從具有子查詢和內部聯接的SQL查詢創建SQLAlchemy查詢。

我正在使用python> 3.5，“ oracle + cx_oracle”驅動程序和SQLAlchemy == 1.3.6

我需要轉換的SQL查詢是：

SELECT DISTINCT d.*, t.max_date, t.USER_ID
FROM DATABASE_ONE d
INNER JOIN (
    SELECT USER_ID, MAX(DATE_CREATED) max_date FROM (
        SELECT * FROM DATABASE_ONE
        WHERE USER_ID IN ('1','2','3')
        AND CATEGORY = 'Users'
        AND IS_DELETED IS NULL
    )
    GROUP  BY USER_ID
) t on t.USER_ID = d.USER_ID AND t.max_date = d.DATE_CREATED

下面是我嘗試將上述SQL查詢轉換為SQLAlchemy查詢的代碼。

    # --------------------- first query -------------------

    first_query = (
        Session.query(DatabaseOne)
        .filter(
            DatabaseOne.user_id.in_('1', '2', '3'),
            DatabaseOne.category == "Obligor Rating Scorecards",
            DatabaseOne.is_deleted == None,
        )
        .subquery("first_query")
    )

    # -------------------- second query --------------------

    second_query = (
        Session.query(
            DatabaseOne.user_id,
            func.max(DatabaseOne.date_created).label("max_date"),
        )
        .select_from(first_query)
        .group_by(DatabaseOne.user_id)
        .subquery("second_query")
    )

    # -------------------- final query --------------------

    final_query = (
        Session.query(
            DatabaseOne, second_query.c.max_date, second_query.c.user_id
        )
        .join(
            second_query,
            and_(
                second_query.c.user_id == DatabaseOne.user_id,
                DatabaseOne.date_created == second_query.c.max_date,
            ),
        )
        .distinct(DatabaseOne)
        .all()
    )

• 我能夠在first_query上獲得預期的結果。
• second_query無法給出預期的結果。
• 我不確定final_query是否正確。

Answer 1

根據您的SQL，我認為您正在嘗試查詢提供了user_id且具有最大日期的行。 所以首先也許我們可以稍微更新一下SQL：

SELECT DISTINCT d.*, t.max_date, t.USER_ID
FROM DATABASE_ONE d
INNER JOIN (
    SELECT USER_ID, MAX(DATE_CREATED) max_date 
    FROM DATABASE_ONE
    WHERE 
        USER_ID IN ('1','2','3')
        AND CATEGORY = 'Users'
        AND IS_DELETED IS NULL
    GROUP  BY USER_ID
) t on t.USER_ID = d.USER_ID AND t.max_date = d.DATE_CREATED

在這種情況下，更容易閱讀並轉換為SQLAlchemy語言。

---

然后，關於第二個SQLAlchemy查詢的問題是，您嘗試從子查詢中進行選擇，但是選擇是從原始表中進行選擇。 如果將第二個SQLAlchemy查詢轉換為sql查詢，則如下所示：

SELECT DATABASE_ONE.USER_ID, MAX(DATABASE_ONE.DATE_CREATED) max_date FROM (
    SELECT * FROM DATABASE_ONE
    WHERE USER_ID IN ('1','2','3')
    AND CATEGORY = 'Users'
    AND IS_DELETED IS NULL
)
GROUP  BY DATABASE_ONE.USER_ID

編寫SQLAlchemy查詢的更好方法：

    subquery = Session.query(
        DatabaseOne.user_id,
        func.max(DatabaseOne.date_created).label("max_date"),
    )
    .filter(
        DatabaseOne.user_id.in_('1', '2', '3'),
        DatabaseOne.category == "Obligor Rating Scorecards",
        DatabaseOne.is_deleted == None,
    )
    .group_by(DatabaseOne.user_id)
    .subquery()

    Session.query(
        DatabaseOne, subquery.c.user_id, subquery.c.max_date # see the .c method to access column in subquery
    ).select_from(subquery).join(DatabaseOne).filter(DatabaseOne.user_id = subquery.c.user_id,DatabaseOne.date_created = subquery.c.max_date).all()