如何修复递归 CTE 查询中的 "near 'with': syntax error" (flask/sqlalchemy)

Question

我正在尝试重现在 SqlAlchemy 文档页面上找到的 this 查询。在 models.py 中设置 Part class 之后，这就是我所拥有的：

from app import app, db, models
from models import *

@app.route('/')
def test():
    included_parts = db.session.query(
                    Part.sub_part,
                    Part.part,
                    Part.quantity).\
                        filter(Part.part=="our part").\
                        cte(name="included_parts", recursive=True)

    incl_alias = db.aliased(included_parts, name="pr")
    parts_alias = db.aliased(Part, name="p")
    included_parts = included_parts.union_all(
        db.session.query(
            parts_alias.sub_part,
            parts_alias.part,
            parts_alias.quantity).\
                filter(parts_alias.part==incl_alias.c.sub_part)
        )

    q = db.session.query(
            included_parts.c.sub_part,
            db.func.sum(included_parts.c.quantity).
                label('total_quantity')
        ).\
        group_by(included_parts.c.sub_part).all()

    return 'test complete'

但这给出了一个错误：

OperationalError: (sqlite3.OperationalError) near "WITH": syntax error [SQL: u'WITH RECURSIVE included_parts(sub_part, part, quantity) AS \n(SELECT parts.sub_part AS sub_part, parts.part AS part, parts.quantity AS quantity \nFROM parts \nWHERE parts.part = ? UNION ALL SELECT p.sub_part AS p_sub_part, p.part AS p_part, p.quantity AS p_quantity \nFROM parts AS p, included_parts AS pr \nWHERE p.part = pr.sub_part)\n SELECT included_parts.sub_part AS included_parts_sub_part, sum(included_parts.quantity) AS total_quantity \nFROM included_parts GROUP BY included_parts.sub_part'] [parameters: ('our part',)]

生成的查询（从错误消息中复制粘贴）如下所示：

WITH RECURSIVE included_parts(sub_part, part, quantity) AS \n(SELECT parts.sub_part AS sub_part, parts.part AS part, parts.quantity AS quantity \nFROM parts \nWHERE parts.part = ? UNION ALL SELECT p.sub_part AS p_sub_part, p.part AS p_part, p.quantity AS p_quantity \nFROM parts AS p, included_parts AS pr \nWHERE p.part = pr.sub_part)\n SELECT included_parts.sub_part AS included_parts_sub_part, sum(included_parts.quantity) AS total_quantity \nFROM included_parts GROUP BY included_parts.sub_part

格式化（为了便于阅读，在不同的地方换行）：

WITH RECURSIVE included_parts(sub_part, part, quantity) AS (
    SELECT parts.sub_part AS sub_part, parts.part AS part, parts.quantity AS quantity 
    FROM parts
    WHERE parts.part = ? 
    UNION ALL 
    SELECT p.sub_part AS p_sub_part, p.part AS p_part, p.quantity AS p_quantity
    FROM parts AS p, included_parts AS pr 
    WHERE p.part = pr.sub_part
)
SELECT included_parts.sub_part AS included_parts_sub_part, sum(included_parts.quantity) AS total_quantity 
FROM included_parts 
GROUP BY included_parts.sub_part

并且，为了比较，这里是纯 PostgreSQL 查询，sqlalchemy 文档 link 到：

WITH RECURSIVE included_parts(sub_part, part, quantity) AS (
    SELECT sub_part, part, quantity FROM parts WHERE part = 'our_product'
  UNION ALL
    SELECT p.sub_part, p.part, p.quantity
    FROM included_parts pr, parts p
    WHERE p.part = pr.sub_part
  )
SELECT sub_part, SUM(quantity) as total_quantity
FROM included_parts
GROUP BY sub_part

我能看到的 Postgre 查询（我认为应该有效）和我生成的查询之间的唯一区别是：

所有额外的 "AS" 语句（SELECT parts.sub_part AS sub_part 对比 SELECT sub_part）
格式不同（生成的查询在奇怪的地方有换行符 - 例如，UNION ALL 和 SELECT 之间没有换行符）

但是，据我所知，这些都不会导致语法错误... 我还尝试将 Postgre 查询作为原始 SQL 执行（尽管 SQLAlchemy 显然使用 sqlite3，但仍然）：

    query = db.engine.execute(\
    '''WITH RECURSIVE included_parts(sub_part, part, quantity) AS (
SELECT sub_part, part, quantity FROM parts WHERE part = 'our_product'
UNION ALL
SELECT p.sub_part, p.part, p.quantity
FROM included_parts pr, parts p
WHERE p.part = pr.sub_part
)
SELECT sub_part, SUM(quantity) as total_quantity
FROM included_parts
GROUP BY sub_part''').all()

但我仍然遇到语法错误。

OperationalError: (sqlite3.OperationalError) near "WITH": syntax error [SQL: "WITH RECURSIVE included_parts(sub_part, part, quantity) AS (\nSELECT sub_part, part, quantity FROM parts WHERE part = 'our_product'\nUNION ALL\nSELECT p.sub_part, p.part, p.quantity\nFROM included_parts pr, parts p\nWHERE p.part = pr.sub_part\n)\nSELECT sub_part, SUM(quantity) as total_quantity\nFROM included_parts\nGROUP BY sub_part"]

我还尝试重新格式化生成的查询并将其作为原始 SQL 执行，结果相似。

最后，我尝试在 SQLite 中编写查询并执行它：

WITH RECURSIVE included_parts(sub_part, part, quantity) AS (
    SELECT sub_part, part, quantity FROM parts WHERE part="our_product"
    UNION ALL
    SELECT parts.sub_part, parts.part, parts.quantity FROM parts, included_parts WHERE parts.part=included_parts.sub_part
)
SELECT sub_part, SUM(quantity) AS total_quantity
FROM included_parts
GROUP BY sub_part

这也会引发语法错误。

在这一点上，我不太确定该怎么做...似乎即使 WITH 具有正确语法的查询仍然会抛出错误。根据文档和此处 (_ 的回答，我知道 Sqlalchemy 支持递归 CTE 查询。老实说，我不知道为什么所有这些查询都被认为语法错误。我的 python 代码与文档中的示例几乎相同。

我需要为 WITH RECURSIVE 安装一些东西才能在 SQLAlchemy 中工作吗？我的语法真的错了吗？几乎迷失在这里，任何帮助表示赞赏。

（正在编辑以将其返回首页。我希望我可以说我已经取得了一些进展，但我现在真的不知道该怎么做。这是 PostgreSQL vs SQLite 问题？有没有人有我正在尝试做的工作示例，我可以看看？）

Answer 1

问题是您运行旧版本的 sqlite3（如#sqlalchemy 中所讨论）；你有 3.8.2 并且在 3.8.3 中添加了 CTE 支持。

如何修复递归 CTE 查询中的 "near 'with': syntax error" (flask/sqlalchemy)

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