Question

我的Django应用中有一个queryset。查询集正在跨多个表访问信息，这些表中填充了产品信息（每个提供商的价格，名称，库存等...您在购物中发现的常用资料相关的应用程序。）

由于一种产品可以有多种价格，所以我最终得到了重复的产品。这实际上是合理且合乎逻辑的，因为SQL只是向我显示与每个产品价格相同的重复产品。

这就是我使用聚合的地方：

queryset.annotate(
   annotate_min_price=Min("product_prices__price"),
)

这使我的查询集仅返回每种产品的最低价格，从而阻止了产品的重复。

此时查询如下：

SELECT DISTINCT 
    "prod_prod"."id",
    ...
    MIN ( "monetary_prodprice"."system_all_included_price" ) AS "annotate_min_price" 
FROM
    "prod_prod"
    INNER JOIN "monetary_prodprice" ON ( "prod_prod"."id" = "monetary_prodprice"."prod_id" )
    INNER JOIN "monetary_pricelist" ON ( "monetary_prodprice"."pricelist_id" = "monetary_pricelist"."id" )
    INNER JOIN "monetary_pricelistdestinations" ON ( "monetary_pricelist"."id" = "monetary_pricelistdestinations"."pricelist_id" )
    INNER JOIN "prodtransaction_carrier_pricelists" ON ( "monetary_pricelist"."id" = "prodtransaction_carrier_pricelists"."pricelist_id" )
    INNER JOIN "prodtransaction_carrier" ON ( "prodtransaction_carrier_pricelists"."carrier_id" = "prodtransaction_carrier"."id" )
    INNER JOIN "prodtransaction_carrierdelivery" ON ( "prodtransaction_carrier"."id" = "prodtransaction_carrierdelivery"."carrier_id" )
    INNER JOIN "monetary_pricelistcountry" ON ( "monetary_pricelist"."id" = "monetary_pricelistcountry"."pricelist_id" ) 
WHERE
    (
        ...
    ) 
GROUP BY
    "prod_prod"."id",
ORDER BY
    "annotate_min_price" DESC

问题在于，除了最低价格外，我还需要获取该价格的实际ID。因此，我相应地修改了查询集：

queryset.annotate(
    annotate_min_price=Min("prod_prices__system_all_included_price"),
    annotate_best_price=F('prod_prices__pk')).order_by(ordering)

这是我解决问题的地方。这将产生以下查询：

SELECT DISTINCT 
    "prod_prod"."id",
    ...
    MIN ( "monetary_prodprice"."system_all_included_price" ) AS "annotate_min_price",
    "monetary_prodprice"."id" ) AS "annotate_best_price" 
FROM
    "prod_prod"
    INNER JOIN "monetary_prodprice" ON ( "prod_prod"."id" = "monetary_prodprice"."prod_id" )
    INNER JOIN "monetary_pricelist" ON ( "monetary_prodprice"."pricelist_id" = "monetary_pricelist"."id" )
    INNER JOIN "monetary_pricelistdestinations" ON ( "monetary_pricelist"."id" = "monetary_pricelistdestinations"."pricelist_id" )
    INNER JOIN "prodtransaction_carrier_pricelists" ON ( "monetary_pricelist"."id" = "prodtransaction_carrier_pricelists"."pricelist_id" )
    INNER JOIN "prodtransaction_carrier" ON ( "prodtransaction_carrier_pricelists"."carrier_id" = "prodtransaction_carrier"."id" )
    INNER JOIN "prodtransaction_carrierdelivery" ON ( "prodtransaction_carrier"."id" = "prodtransaction_carrierdelivery"."carrier_id" )
    INNER JOIN "monetary_pricelistcountry" ON ( "monetary_pricelist"."id" = "monetary_pricelistcountry"."pricelist_id" ) 
WHERE
    (
        ...
    ) 
GROUP BY
    "prod_prod"."id",
    "monetary_prodprice"."id"
ORDER BY
    "annotate_min_price" DESC

这使我的查询集重复了产品。我知道发生这种情况是因为我要PostgreSQL将ID的价格加到每一行（产品），并且以某种方式破坏了MIN的聚合器。

我的问题是：我怎样才能让Django只同时退回具有最低价格和该价格ID的产品？

Answer 1

您可以使用子查询

$userid=$_GET['user']; 
/////then run below query (leaving out mysqli function)
UPDATE users SET confirmed=1 WHERE user_id='$userid'

以下解决方案无法按照注释中的说明进行操作，因为您无法在过滤器中引用窗口功能

您应该可以用最低价格注释每个产品

min_query =
    ProductPrice.objects.filter(product_id=OuterRef('id'))
    .order_by('system_all_included_price')
    .values('system_all_included_price', 'id')[:1]

queryset.annotate(
    annotate_min_price=Subquery(
        min_query.values('system_all_included_price')
    ).annotate(
    annotate_min_id=Subquery(
        min_query.values('id')
    )
).order_by(ordering)

如果在某些情况下价格可以相等，那么您可能想再次遍历带注释的分区，以识别出最低的ID，然后根据匹配最低的ID进行过滤。

queryset.annotate(
    annotate_min_price=Window(
        expression=Min("prod_prices__system_all_included_price"),
        partition_by=F('prod_prices__pk'),
        order_by=ordering,
    ),
).filter(annotate_min_price=F('prod_prices__system_all_included_price)

使用注释和聚合而不会重复

1 个答案: